I think the main reason is that the guy he's been compared to since day 1 is the prototype for being a flashy player. Say what you want about there being no Crosby vs. Ovechkin debate, but you can't think of one without the other.
Ovechkin hits everything you'd look for in a flashy player: speed (and the fact that his short, choppy strides give it the impression that he's even faster than he actually is), dekes, snipes, general focus on goal-scoring, big hits, even celebrations if you want to go that far. Crosby is a far more cerebral player in general, but the comparison that was always pushed made it feel like he was just a brain on skates.
Realistically, Crosby is flashier on a more consistent basis than anyone, it's just more subtle/nuanced. He's also more economical/efficient than anyone offensively, but that doesn't mean it can't be flashy as well. The things he does with his skating/footwork, passing and puck protection alone are very flashy, but he's not known for the big splash plays like big hits or snipes, which is what most think of as flashy.