UFC is ALL martial arts rolled into one. Those fighters don't learn just one fighting style, like kickboxing or judo, they learn all of them. Some fighters are stronger in some fighting areas than most, so they tend to stick with that particular style, but still use all the styles they learned in training.

The knockouts I've seen have not been lucky by flying fists. I have seen a lot of knockouts by 1 straight shot to the jaw, not by swinging like a madman and ladning a lucky shot.

I'm not sure what UFC you're watching man, but there are plenty of skilled knockouts.