When I am driving, safety on the road comes first, so if I see you wave and I do not wave back, my preoccupation of the road, a turn, or something is why I don't.
I do not look for others to be waving at me, just not thinking about it, but if I see you wave, I wave back.
Then that gets me to looking out to wave at you, then when you don't, well, let's just say it's not that big of a deal, lol.
I have been a motorcyclist for many years, still am, and generally always wave at other bikers on the road, unless I need both hands shifting gears, maybe turning, or sitting at a stop holding the clutch.
With all that said, I will say something about the "biker" wave, and look for those who reciprocate correctly.
For those on two wheels, it is with the left hand, two fingers pointed down like an upside down peace sign.
The meaning is a wish of good will representing: Keep two wheels on the road!
Not sure how to wave 6 fingers at the MotorHome drivers, maybe 5 on one hand and one on the other, just kidding!
Have a nice day,