The other factor that you left out is the inherent laziness of most people.
And as I've mentioned earlier their disbelief that it can actually be done with a little advance planning.
My sister is currently in the US and wasn't interested when I suggested she check her seat allocation. No idea where she ended up but it would've been better with a little advance planning. Didn't believe me that you could choose at T-24.
Ah well her loss. My upcoming US trip is well planned with flights and seats chosen, a little status run to attain LTG. The rest of my trips are to places I want to see. All done quite cheaply thank you thanks to AFF and its well informed members.