Craig, y'know you're right, even though my awning isn't attached to my camper. Why is that, I wonder?
My Theory: It's related to the reason that motorhomes, camping trailers, XP campers, etc. have their main/cabin entrance on the passenger side. If you pull over to the side of the road to hang out for a while you don't want to enter or exit the cabin on the traffic side of the rig (the driver side). And if the main door is on that side then it makes sense that you'd want the awning to be over your "front porch" on that side, too.
Yes, the FWC and ATC don't have their doors on the side...but because the right/passenger side is the standard side for awnings on other types of RV (because their main doors are on that side), the manufacturers put them on that side anyway.