I pretty much asked myself the same question ever since I got the Wii. I wanted many games that were on PS2 (I owned a GC before) that I wanted to play and saw Nintendo's console as a good opportunity
However, while in theory it would have been a good idea. Sometimes is not as simple as we think.
A port has to justify it's purchase, specially if it was a PS2 game released years back. Just by making it work on Wii and add the Wii Remote Nunchuk controls does not guarantee a hit, there needs to be more content in the game. This requires extra work from the developers and the publisher. The majority chose to move to HD completely.
The second issue is the question: "will the audience like the game if we port it?". Some games, even if they were good on PS2, won't be well received on Wii for many reasons: the fans went to PS3 and Xbox360, the new audience might find the game disturbing, or other reasons.
I say some developers were dumb to not port to the Wii because their games could have benefit from that, while others did the right thing to not port their games because they won't sell.
I don't think GTA games would sell on Wii as many expect.
