why do exes want to be friends?

my ex is trying real hard to be friends but idk if i can...i still like him a lot and he knows it. he broke up with me and was disrespectful to me for the longest time. he constantly apologizes because he keeps messing up. we get along really well except we have a hard time connecting emotionally...the way he reacts to things makes me feel like he's selfish and the way i react to things makes him feel like i close myself off. it's driving me nuts because while i want him in my life because we have so much in common and i feel like i can talk to him about things a lot of people won't understand, i love him because of those things and we can't be together. why do some people try so hard to be friends with an ex? has anyone dealt with a situation where you feel like you've found the male/female version of you but for whatever reason, being together won't work? how did you cope? did you remain friends?