That's because everyone's incompetent. Most of the time no one has been trained properly, or it's bad management at the McDonalds. When I get an order 'wrong' it's because it's some foreigner who can't speak english properly, or they shout into the speaker box and I mis-understand them. You also have to consider a lot of other factors, if it's busy or not.
But bottom line, nah they don't deserve a raise, the jobs easy as fuck.