I believe that this issue is mostly due with them, although there are some qualities of ours which cause them to become obsessed with us. The reason why narcissists become so obsessed with us has more to do with them, than it does to do with us.
They are insecure and have an inferiority complex. They have very low self worth, self esteem and self belief. At the beginning of the relationship they specifically chose us for our empathic qualities. In their minds they were thinking "Yes, this person will give me the attention, validation and approval I crave. This person will make me feel strong and confident". They cannot validate themselves from within. This is why their self worth, self esteem and self belief is so low. They require an external source to do the validating for them and that's where we come in. The problem begins once we start to see through their bullshit. We realise that they are only with us to obtain narcissistic supply and once you realise this fact, you are going to find it very difficult to continue validating them. They have got it in for you right from the first narcissistic injury. Once they see that it's game over, they will never see you the same way ever again. From this first narcissistic injury, they are going to do whatever it takes to destroy you. They become obsessive stalkers. Doing everything they can to devalue, humiliate, and exploit you. A normal, emotionally healthy person does not experience a narcissistic injury. If you do something that hurts or offends them, they will acknowledge this and then want to resolve it with you. The narcissist does not know how to do this, they cannot self-reflect and they cannot resolve anything. They will become bitter and resentful. They will hold a grudge for years and never let go. The reason for this is because the narcissistic injury creates intense hate, anger and envy within them. They don't know how to deal with their emotions, so they take it out on you, again and again for as long as you are around them. They don't know how to stop. They have the maturity of an emotional toddler, so they will react and retaliate in a similar way. They are so competitive and think you are better than them, to the point where there's not enough room for both of you in this life. So now you have to die, you must be destroyed. Suddenly you realise that this tough, confident and charismatic exterior was really just a mirror and an imitation of your good qualities. But they don't want to see you shine. They want to see you crushed and broken, with nothing and no one. Because they are extremely hateful, angry, envious and jealous individuals. They hate your good qualities because they cannot have them, they cannot sustain them for long periods of time. This then makes them very frustrated and resentful towards you. They become envious and try to destroy your good qualities, your career, finances, friendships and any potential relationships. It doesn't matter if they have one of the same things that they are trying to destroy in your life. They are always comparing what they have with what you have and it can never measure up. They see you as being happier and more fulfilled than they are. They see you as being more motivated and satisfied with your work than them. You have more money, your friends are genuine. Your relationship partner is better looking than theirs. Whatever they have, it does not matter. They can never be fulfilled or satisfied with anything in life. No matter how great something is, they will always take it for granted. It's like giving a $100 bill to a toddler. Do you really think that toddler is going to understand and appreciate the value of that $100 bill? No, of course not. They are just going to tear it up and then move on to play with one of their toys. And it's the same thing with the narcissist.
They cannot be fulfilled or satisfied with anything for long, no matter how great it is. They do not have the capabilities to be genuinely happy or experience a deep emotional connection but we do have the capabilities to do this and that's what makes them so mad, that's what makes them so envious of us. They know that no matter how badly they complicate our lives. We will always get back up, re-build and move on. They know that we have the capabilities, all of the good qualities, to live a happy and fulfilling life. They know this. They are also very aware that they do not have the capabilities or good qualities to do this. So they become obsessed, trying to sabotage and destroy everything in our lives. Because they know that they can't build anything great in theirs'. The narcissist knows that no matter how much they focus on their lives, no matter how much time, energy and effort they put into it.. it will never amount to anything great. They know that if you do have the time, energy, effort and focus on your life... you could achieve anything, things that they could only dream about. And this is why they will go out of their way to take up your time, drain your energy, laugh at your effort and do anything they can to take your focus off of your progression. If they knew that you would never amount to anything great, you would never find a real loving partner and have a great life. If they knew that you did not have the capabilities within you to do this. They would just leave you alone. They have no light, they cannot shine, so you shouldn't either. That's how they see it. The narcissist has no ability to shine on their own, their light comes from external sources such as attention, validation and admiration. Or they will shine at the expense of someone else, by tearing them down. They have to do this because they cannot generate their own light. All they can do is reflect back our own light, like the moon reflects the light of the sun. They know that we are different in a good way and we stand out. It is a reminder to them that they are nothing special and it triggers their inferiority complex. They will insult you about things that make you unique, anything that makes you attractive in any way. They don't want you to be unique or attractive.You stand out and people see you. Outside of their flying monkeys and controlled environments, people will admire you and validate you as a person. And they know this. That's the whole point of the flying monkeys, smear campaigns and controlled environments. To regulate the excessive attention, validation and admiration you would otherwise be receiving. Remember they are very hateful, angry and envious people. They do not want us to shine. They do not want us to be validated and admired. They have seen enough of your good life, positive qualities, hard work and attractive partners in the past. The whole purpose of their obsession and control is that they are trying to prevent this from continuing. They will become obsessed with your past and begin re-writing it. Now you are being told that you never had a good life, positive qualities, you never worked hard or had any attractive partners. Good example of gaslighting. Yes, they want you to see yourself differently. They know that you have deep self love, they know that you self-validate and approve of yourself. But they want it to stop. And that's why they will become obsessed with you, to dig up any dirt they can find. Anything that makes you undesirable or not good enough. They will do everything they can to project their negative emotions on to you. I am sure you lived a good life and had many good things going on before the narcissist came in and got mad and envious. There is nothing the narcissist hates more. It reminds them that they are not attractive and they are not receiving as much admiration and validation as they would like. This is why they will do whatever they can to prevent you from attracting anyone or obtaining any admiration. Such as developing an obsession with you, so that they can find something undesirable or flawed about you. Or enforcing their flying monkeys and creating smear campaigns. These are all designed to isolate you and prevent you from becoming your best self. Narcissists are their worst selves... they cannot just let you leave their pit misery and be everything that they always wanted to be.