"Mario is a very important character in the Nintendo world and so we want him to appear in our titles.”Maybe it's a bit late for this as we have seen Mario star in all sorts of games since his first game, being his image one of the most repeated characters in the videogame world (if not the most). However, he has a point as too many titles would almost certainly have the character lose all appeal.
"Indeed there are a lot of games to which he is well-suited. However if he appears in too many games then they will lose their uniqueness, and so with that we are very strict when choosing which games to have Mario feature in."
(They released Mario fucking Paint and Dr fucking Mario!! - Ed)