Not a farmer, but from my little knowledge, I believe animals are also bred for docility, disease-resistance, and growth rate. The latter two in particular are likely higher priority than flavor. Consumers don't seem to price discriminate on meat flavor very much, so the animal that puts on the pounds the fastest makes the most money.

My family does small scale cattle ranching - we do end up selecting for some combination of dumber and more docile, just by getting rid of any cows that are aggravating ringleaders. Sure they're mostly happy, but the grass is greener on the other side of the fence, or you're weaning, and then it's really nice not having the ones who'll break free and take everyone else with them.