Why do men cheat when they just feel guilty afterward?

Some don't.

Usually one would cheat, if they didn't feel content somehow in their relationship or the relationship isn't as exciting any more.

It varies from circumstance to circumstance.

ANSWER:

The truth of this question will rely on the married man, why? let me guide you to that direction. When most married men find another woman that will meet his needs, ( it's okay if he doesn't think about his wife's need) there's no such things as feeling guilty or even bad when it comes to what this married man is doing or done. It's only natural for a married man to feel guilty because his affair was caught, if it didn't his life with the other woman will be perfect.