Why when most want to break up they just vanish or hide from you?

Breaking up is a difficult decision even for the one initiating the breakup. Many would just prefer to hide from it. Also, many really don't want to hurt the other person regardless of the reason for the breakup. I'm not saying it's a good excuse. It's always better to be respectfully honest instead of dragging it out.

I've never experienced that tbh. My last ex broke up with me but wouldn't leave me alone, for years, it was torture, I couldn't get over him

Normally it is because they don't know how to communicate knowing that the person will get upset and they are cowards. Some believe that they save the person from heartache, but they are just being selfish

Simply put, they are cowards..