At the same time, demanding is not the same as deserving. If a dispassionate analysis is done of UK and its competitors, considering every factor and precondition of success in college football, there's no way to slice it in a manner that doesn't place UK at fifth in the current SEC East in the so-called natural order of things. The other schools sans Vanderbilt are either in states with better recruiting bases, or they simply and ultimately care more about football, or both.
Those things are flipped in basketball. Kentucky fans are very demanding, but it's the demanding of the spoiled, not the demanding of the unreasonable. UK has the history, the tradition, the brand name, and all of that flows from the unquestioned need to win in hoops that no other SEC school has. They should win and everyone knows it.
So that's the thing. As a whole, UK fans want to win at football. They don't desperately need to win. Which is why they are, as you put it, accepting of mediocrity. The other thing is, even if they decide not to accept it, if they decide they desperately want to win, that still won't change their natural place on the food chain. There's not a lot they can do except endlessly cycle through coaches waiting for the bolt of lightning to strike.