Why?
You seem to be forgetting the basics of economics. It really doesn't matter what you think they "deserve" or how hard you or they think it is to deal with the general public.
What matters is how many people could/would be willing to do their jobs. And the answer is quite a few, whereas there are many fewer people who could manage a McDonalds.
Thus demand is low for flight attendants, and thus the price is low.
I'm all for people negotiating for as much as they can get, but I certainly don't think it's ridiculous that the market offers different prices for different services.