Some people like the excitement of infatuation more than actually being with someone.
I am in no way excusing this behavior but it goes back to our "non-evolved" animal side. men's job is to impregnate as many women as possible to ensure the continuation of the species and womens job is to pick the one man that will ensure the survival of the children.
They have a limited attention span.
I have no idea, like how a man can have the most beauiful woman in jeans and go for a hooker down the road. Men are strange creatures, I'm going to learn how to play this game without having to give a thing...
They have no staying power...
I hear that a lot but I have never met anyone that was really like that so much.
We're all different. 6+ billion on Earth means 6+ billion ways of perceiving reality.
Because they got bored. The trick is not to let bordom set in