I like how the title implies bad and casual are synonymous.

The thing is: People with bad attitudes have bad attitudes. What skill level they have is largely irrelevant to that.

What does a player with a bad attitude do when he's matched against someone worse than him? "Pwn" the newbie, tell him how much he sucks, give him a teabagging and do rape and mother jokes.
What does the same player do when matched against someone better and getting "pwned" himself? Blame hacking, a broken mouse, bugs, the enemies strats and whatnot. Or, in a team game, the jungler.

You can give people tons of excessively detailed numerical feedback on their performance and all they'll do with it is to either use it to stroke their ego or rationalize it away if they have such an attitude. People with bad attitudes don't care about the facts, they care about their ego. Even in 1vs1 games, people will find something but themselves to blame for the defeat.

That said, players with such an attitude are more prone to be bad and players with good attitudes are more prone to be good. The reason is simple: Accepting blame doesn't feel good. People with bad attitudes thus will push the blame away from them to avoid it, while people with good attitudes will accept it and try to reduce their share of the blame, thus easing the feeling, by contributing more.

One last note: "Elitist" usually refers to people who think they are good and expect others to be good, rather than good players. You can be an elitist and still suck, which renders you a hypocrite.