Because he's considered one of the ultimate style-over-substance directors - the more distinct (and over-the-top) a director's style is, the easier it is for them to divide or alienate audiences. It also doesn't help that his best-known Hollywood movies already tend to be some rather absurd-looking projects like Hard Target or Face/Off so Western audiences come away with this impression of him being a borderline Michael Bay kind of director (and they might well get that impression from something like Hard Boiled anyway).
Besides, I think you can definitely make the case that M:I-II wouldn't have been significantly better (if at all) with a director other than Woo anyway.
Pretty much this.
Woo's trademark is slow motion.
Slow motion walking shots
Slow motion high-kicks
High octane chase scenes that are bookended by slow motion vehicle stunts
Slow motion doves taking flight in any shot that's leading to a slow motion action scene
Protagonist jumping through the air, firing two guns, in slow motion
And sparks. Sparks everywhere when there shouldn't be sparks: Whenever anyone shoots anything at any time with any kind of weapon, the object that is hit, no matter what it's made from, throws off showers of sparks, in slow motion
And pan shots and crane-zooms. During a fight between protagonist and antagonist, the camera always zooms in... from miles away, and 150 feet up...