When Kingdom Hearts: Birth by Sleep released last year, it was noticeably missing from the PlayStation Network. It only received a UMD release, meaning PSPgo owners couldn't play the title.
Tetsuya Nomura, the series' creator, won't really explain why though, as when quizzed about the subject he said "It's difficult because of a reason I cannot say." He did state that he is trying to find a way to make it happen, but he needs more time.
When Kingdom Hearts: Birth by Sleep released, we gave it a score of 9/10 - high praise for one of the most recent entries into the franchise.