I didn't hear a single thing about the game until after it was already dead, and that's why I'm not surprised it flopped.
If they'd done better(read: any) marketing or public testing, then it might have been at least salvageable, but from what I've read it seems like people weren't fans of the character designs and gameplay either.
Calling Taco Bell tex-mex is dubious at best, as well! It's definitely inspired by it, and has had some influence on the restaurants since; but it's far too fast-food-y to be considered proper tex-mex. TB is in a category all its own creation, which is definitely not a bad thing.