Another theory is that many drivers simply don't see us as a threat. Thirty some years ago the California Highway Patrol was riding big Kawasakis (think CHIPS) A motorcycle magazine took identical bikes, one sporting CHP colors and another in bright red, and took them out on the streets. The red one was cut off and otherwise "disrespected," while the CHP looking bike was treated much better. Not scientific but still very interesting.
Yep, the idea that the smaller the oncoming vehicle is, the less threat to one's continual existence (life) if things go wrong and there's contact made with it, has always been what I have believed lies closest to the crux of this sort of thing.
It's almost a "primordial" phenomenon and how early humans might have thought that the larger the animal they'd encounter in their daily travels would represent more of a threat to their lives than would a smaller animal, and thus then the tendency to discount or even ignore the smaller creature's presence.
(...nope, and also not "scientific" either perhaps, BUT this has been MY "theory" on this matter for some time now)
