MKDA was actually pretty decent (and the Xbox port was sloppier than the GCN port, the Xbox version had a glitch where Frost could lock up the game by doing a Ground Freeze at the same time as someone else did a special attack), and I think it sold pretty well (maybe not as well as the Xbox version, because of Gamecube's positioning at the time, but close), but as for the rest of Midway's lineup, yeah.
The worst part is they don't understand why lazy ports of 2-3 month-old games aren't selling well... so people not only had to wait longer on something (during which they probably gave up and got it for another console or played a friend's copy), but we don't even get an optimised product for the extra time we wait. Gee, Billy (no reference to this site's now-retired leader), I wonder why Gamecube sales of a game are piddling in comparison... The only people that wait are those that don't have a second console, and really, most game fans can't be single-console gamers anymore, the market's changed too much. Two years ago I thought I'd be GCN-only. Today I have a PS2 and an Xbox as well. (Although I admit the Xbox does not get much mileage at all, and I'm not lying to "save face" or anything.) If you want to play the games, you have to go where they're available. So many gamers already have gone two-console or have a friend who's console they use.
So that's possibly why Xbox sales are inflated (it's harder to notice with the PS2 sales) versus the GCN sales, because half the audience who would've bought it on GCN had it been available at the time said, "To heck with it, I'm not waiting," and bought it on one of the other two consoles. And after they get into the trend of doing so, they don't stop when Midway finally releases one GCN port on-time with the other two releases.