One of the only great things about breakups is that you’re really not culturally expected to maintain a friendship with that person. You could have spent every day with them for years, and if they break up with you, you have every right to literally never talk to them again. I have been friends with exes, and I know a lot of people who have prosperous friendships with exes, but maintaing that relationship can be a real hassle. There’s so much baggage that you don’t have in a normal friendship, and so many things you can’t talk about as you would with a friend you’ve never dated. Also, it’s so much easier to slip back into the same old dynamic if you maintain contact with someone that you’ve severed romantic ties with. For some people who can’t move on, that’s a feature. For most people, that would be a bug.