According to an NGamer article (via GoNintendo), Phoenix Wright was originally slated to apply his brand of word-fu to the fisticuffs of Tatsunoko vs. Capcom. However, the iron-willed lawyer didn't make the cut. Why not? Ryota Niitsuma, producer on Tatsunoko Vs. Capcom, explained.
"Because Phoenix Wright only has one move, 'Objection,' we struggled. We designed a move for him: when he says objection, the actual writing attacks the opponent," he said.
"However, 'objection' in Japanese is 'igiari' - it's four characters, whereas 'objection' becomes ten. When we localize, the balance of the game gets destroyed because the move becomes bigger. There'd be no way of avoiding it! We had to remove [Phoenix] for these reasons. In the future, it is one of our aims to get him in."
So now you know.