Why don't women in Mexico and South America have children there?

I mean why the mad rush to America to have Anchor babies.Haven't women in those countries been having their kids there for thousands of years?Its for the welfare we give them here isn't it?I know that 7 out of 10 hispanics in labor at the hospital that I work at are illegal.Whats up, do they have to swat, push out baby and then go home to make supper for the family.