Plenty of seeming nice guys have done some not nice things that they have yet to realize really aren’t so nice.
That’s one thing.
On an entirely different planet are the guys who are “nice” until you ask them to do something they don’t want to do, such as: sweep the floor; do the laundry; stop asking for sex; clarify their own wishes in a relationship; generally communicate directly and adequately.
Nice guys don’t want to communicate clearly.
They don’t want to be heard or understood for what they feel and think.
That’s not what they’re about.