Minimal wages is relative. I imagine that most people do it because those wages let them support their families and build a house / start a business back home. The crossing takes about a year to pay back, and there are living costs, but many work double shift at different jobs, with one paycheque going for living costs in the US and the other for savings/family/setting themselves up for a better life back home. 5-6 years "echando ganas" and you can be set for life. It's a pretty rational thing to do, much like pensioners who retire "down south".