That's more than the minimum wage where I live, and I am in Europe. I suppose there are many countries with people that would be happy to work for that rate.
From what I've read, there are 3 popular demographics that are happy working on MTurk: 1) People living in areas where a non-strenuous, $5/hour is hard to come by. 2) People who are bored and find MTurk a somewhat interesting way to make some spare cash (stay-at-home parents, elderly, students) 3) People who are bored of sitting in front of a screen at work all day with nearly nothing to do (security guards, cashiers) and could use some extra cash