Probably because they have no fucking clue what healthy and producive social behaviour consists of, combined with having never dealt with their feelings in a constructive way once in their whole lives.
It's like they don't know that their behaviour is a telling sign they have some fucked up personality issues to deal with and that no good person ever would consider dating some on-and-off psycho with no emotional self control. Imagine being with someone this clueless your whole life.
My ex (broke up with him because he was obsessive, creepy and couldn't make decisions for himself AT ALL) did this too. He used to call me just to tell me what a "lying fucking whore" i was , one hour later texting me "you are the love of my life, don't u see we belong together, please i'll do anything for u" etc, then wondering why i didn't want to get back together with him.
The logic of these men amaze me, it's as if they lack consciousness completely. Like an amoeba.