The only two GameCube games I'd want are Pikmin 2 and Chibi-Robo. They are already a part of these re-releases, they just haven't come to North America... yet.
With the structure of Mario Golf: Toadstool Tour and its meter swing system, it wouldn't translate to a Wii control scheme as it couldn't simply replace buttons with motions like Mario Power Tennis does. The swing engine would have to be built from scratch, and if they're going to do that then they might as well create a new game.
I assume the NPC games are released at budget prices of $29.99, but what if they pack-in 2 games for the price of one standard game?
The problem with that is if people want just one of the games, they'd have to spend more on something they don't want.