There are many different reasons, some of them can include
I welcome your thoughts, let me know if you want to talk more.
Not every person is the same. Not every persons motives are the same. So I can't give a reasoning for why every man does the things they do.
Some men meet a woman, and everything seems right, they love her and don't want to hurt her or leave her, but perhaps he meets someone who he is sexually attracted to but doesn't want to give up his life for.
Another man may have a history of cheating, whether or not he's ever been caught at it is irrelevant, but its not usually something he can stop, even though he says he will every time.
You have men who are sex addicts or egotistical and simply don't care who they hurt along the way.
There are so many different scenarios, it would be impossible to cover them all. Is there a particular situation you would like to discuss?