The geometry of bikes like Harley's aren't conducive to fast response/handling, and their brakes aren't really too flash. Floorboards extend out so they hit the pavement when lean angle increases (most bikes the side stand would be the first thing to hit at lean) So you get a lot of novice riders that want to become "bad boys". They go their Harley dealership, hand over 10,15, 20K or more, get a bike that's very torquey, hit the open road, and then either they a) have no idea about counter steering and when they come to a sharp bend they turn the bars as you would if you are driving a car....bike does the opposite of what the rider was expecting and they go off the road, or b) car turns left in front of them, they lock up the rear brake and fail to use the front (where 75% of the max braking potential is) and slide right into the vehicle. Generally speaking of course.
In regards weight, there are 1000cc sportbikes under 400lbs, and 750cc cruiser like mine that are 550lbs or more. I would expect more wind "pushing around" a lighter bike, it's a matter of counter steering into the wind but when the gusting is intermittent that can be an interesting journey. The cross section of the fairing etc can also have a lot to do with it, and if the rider is sitting upright or hugging the tank.
