Why do some people avoid closure after a relationship has ended?

Fear

Fear is behind most everything holding people back from thier own growth, potential and happiness.

If the relationship is over, get on with your life and get over it. Closure is usually something that women need to understand why they've been dumped. Nobody knows why men do the things they do. Even most men don't. If somebody needs closure it's only to try to analyze themself and the other person in the relationship. Move on and don't turn it into a science project.

I can only speak for myself. When a relationship ends, either ended by me or partner, I consider it finished...period. I will put the other person out of my life completely. They will cease to exist in my mind. So, when it ends - get over it, get on with your life, & forget about it. No power play, just the way I like it.

The reason I never opted for closure with my ex was that I always hoped we would have another chance, like she would change her mind or something. And also because I feared I would never find anybody to be with again.

It could have do with abandonment issues. Or dependancy issues.

Some people don't know how to end a relationship with anything but hurt-feelings.

It may be that they cannot deal with confrontation well. Introverts typically avoid confrontations.