When one has done multiple wrongs to another, wrongs that a simple 'my bad' is not enough, and especially if to someone who has done them no harm, it's very difficult to admit they were wrong.... because to admit they were wrong is to admit they are not a good person. That is a delusion that most people cannot admit to themselves, i.e., that they are not a good person.... as well as to become the good person they want to be, they either have to humble themselves (usually) or there is penance required.
this is all true...and when a person can do this...that's when they are truly an adult.