From what I heard, BMX XXX was crap anyway.

Most M-rated games that focus on gratuitousness (language, sex, violence) are crap. (Even I dislike Conker's Bad Fur Day, at least in comparison to the Rare's less-linear, more-stuff-to-collect N64 adventures that didn't seem to take as long to develop.) Immature is more accurate.
GTA (especially III) was a big deal at the time, but it was one of the first "sandbox" games that really hit it off. The option to be bad was there, snipe random people, have a prostitute restore your health, etc., which is what the big deal was, I guess. Then there was that whole San Andreas "Hot Coffee" thing but for the most part its peak (in controversy and even popularity. I'd wager) has passed. I've played some of III, I'm guessing that the GTA games since then have added a lot of features, so it doesn't fall automatically into my M-rated-for-gratuitousness-so-it-must-be-crap filter. (And I know San Andreas is now AO but whatever.)
And even if it was/is crap, well, it's crap that sells. We may like to think Nintendo has higher standards than the competition but, and Reggie's interest confirms this - they aren't too high and mighty to pass up a franchise with the selling power of GTA.
(Doesn't GTA stand for "Greater Toronto Area"? Do non-gaming people living in Ontario get confused when people say "GTA's so violent!"?)