Part of the reason is that we don't know much about the man. He was a carpenter, which at that time was more of a catch-all term for any sort of construction. He was pious. He took care of his family, even fleeing his home and becoming a refugee in a foreign land. And by the time Jesus entered His ministry, he was gone, presumably dead.
As a teacher, I know that a great deal about parents can be learned by interacting with their children. Thus, we know some of Joseph because of what we know about Jesus. For that reason, I like to think of Joseph as a kind and caring man who demonstrated for Jesus how to treat other people, how to avoid judgement, and how to be forthright and sincere.
Whatever kind of father he was, we know that Jesus turned out better than any earthly father could have expected. I like to think that the two of them hang out in heaven, enjoying each other's company while talking about the future that is being built.