Your question, basically, is Why don't people act in their own best interest when it would be so easy to do so? To put it mildly, there is no easy answer, and FF programs are certainly not the only place we can observe this "phenomenon." But to hazard a guess: It doesn't take much knowledge to know that participating in FF programs is a no-brainer, but if you don't have that knowledge - or if you believe that obtaining that knowledge is costly and/or difficult - then you may very well be dissuaded from arriving at the "proper" conclusion. Seriously, though, would it be better if everyone joined these programs? I think not. At the very least, it would create even greater liabilities for airlines, hotels because of unused miles; at worst, it would decrese the availability of already scarce awards... I say let sleeping dogs lie...