I am sorry-but"every FF seat=lost revenue"is pure nonsense.
The airlines are making huge profits on FF miles by selling them to every possible co-brander out there.It really is a patsy scheme where you are suckered into getting this credit card or that one,get this rental car,stay at this hotel-all of which(and others)are paying for those miles.And then you go to cash in your horde o' miles and are told "sorry"none of those seats are available"but you can use them to fly from Burbank to lovely Fresno-only 25,000 miles-oh wait-you want to do it this weekend?That'll be $75 cash please."
If they were not profitable they would not be so many out there up for grabs.