Why every flight in the US doesn't have wifi is a mystery to me. Is there any cost to the airlines at all? I'd think it would eventually be a profit center, or at least cost neutral.

If I had a choice between a FC seat, but no wifi, and a coach seat with wifi reasonably priced ($10-$15)... I'd pick the coach seat about 1/2 the time depending on route, time of day, work needs, etc.