C'mon people: This is
NOT complicated. There is no secret answer that needs to be addressed by some PHD who will never get near a Biker...because they are afraid.
Bikers putting down the boulevard are doing only ONE thing, and that..In their mind is just LOOKING GOOD. No more complicated than that.
They are part of a BIG group..BUT, they still have the need to be
individual persons....to stand out in the group. Maybe the babe on the back will take off her shirt..
Custom airbrushed artwork on the tank and fenders...Are BIG. Anyone can do loud pipes and extra chrome.. First..Artwork on a relatively stock bike and then..... if you have a few extra grand..a totally Custom Bike built to order from the ground up.

I can speak of this because I have a few miles under my butt.

NB
Just to set the record strait..I am not a Biker. I am a Motorcyclist.