Bioshock 2 on Wii would probably bomb, which is the problem. Take Two can't forecast the sales numbers to make it worthwhile. From 360 or PS3, bringing a game to Wii would require creating it almost from the ground up. It'd be like creating a new game as far as company resources go, so it's still an investment.
Worse, being a port, waggle controls would be non existent or tacked on, so the game, no matter what series, will always seem inferior to its HD cousin. For multi console owners, that means never buying the game for Wii and that further slashes the target audience. It's not profitable.
Franchises like Rockband, Guitar Hero, Madden, WWE Smackdown and Call of Duty show there's hope, but in every instance (a case could be made to exclude Madden), the games lack something from their HD counterparts. And the sales still reflect this.