I think most have already said what needs to be said about Japeth but just so I can get it out of my system, here goes another opinion on the matter.
Being a great potential talent attracts all kinds of characters and opportunities. Japeth, it seems always decides to go with whatever's he feels best for himself. He went to Ateneo because Norman Black was going to be a great teacher. He transferred to Western Kentucky because the competition was going to make him better. And he came back here because he felt he was the best young prospect who had Filipino blood.
When he first moved back, I'm sure he felt very wanted. The PBA, Team Pilipinas, agents, coaches, teams, etc. all wanted a piece of him. A young guy getting pulled in different directions can get a little confused as to what he wants. I'm sure he wanted everything that was offered him.
My general gut feel is that he did not enjoy playing for coach Yeng Guiao. Yeng is a love 'em or hate 'em kind of coach. He is known for yelling at his players, saying harsh things as a motivational tool to push them. Problem in this case is that Japeth had other options. So given the choices, he will always opt for what he feels is best for himself, not necessarity what's more popular. Some people just don't like getting yelled at I guess. I'm sure other players don't like it either. Difference is, the other players don't have a choice.