Oh, yeah, I guess I should stop listing information as if Wario is supposed to be generally defensive/reactive instead of blindly offensive like an idiot on Wi-Fi.
(For those of you that don't sense sarcasm, it's plainly there.)
Side-B isn't instantaneous, and isn't too difficult to avoid. Because of Wario's horizontal aerial mobility, a "U-Air to B-Air chain" is easy to avoid. If you F-Smash on the landing, Wario will either just keep moving away (like he should be doing anyway, because Falco -should- be giving chase with something other than F-Smash) or double-jump and punish.
Hell, Wario might attempt to predict and get a free aerial, Bite, or Waft, none of which Falco would like.
Like I said earlier, fighting Falco is usually momentum-based; if Falco doesn't get the grab, he's forced to use his B-Air, N-Air, and D-Air for damage, which doesn't work particularly well against Wario. Wario almost only needs prediction for approaching, because his range is terrible. It's not incredibly hard for Wario to run away from anyone. It's quite difficult for Falco to get anything but a well-timed U-Smash for the KO, which is made exponentially harder if the Wario is making good use of his mobility for defense.