If people don't like America, why do they stay?

There is opportunity for them here. In their native country (depending on where they are from), they may not have the opportunity to go to school, or yet, they wouldn't dare say the sh!t they tell you while in their country; they will get beaten, kicked out of school, or some sort of harsh punishment. You are right...they felt this country was worth coming to so that's why they are here.