Does anyone know why everyone on "sons of anarchy" are all missing their right mirror on their bikes?

I might have thought it was because a bike or two was dropped during
filming, but I've started to notice that its everyones bike on the
show, and just the right and not both mirrors... anyone know why? Ive
been riding a motorcycle for years, and I've yet to see this before.
(they do take off both mirrors and directionals durning msf learning
functions, but those always take place in a parking lot since you need
mirrors and turn signals to ride legaly on the street)