We live in a cognitively assorted economy and half of all people have an IQ below 100. 5% have an IQ below 70. If they have unusually pleasant personalities, they may find jobs in the service industry. But most won't.

We have a historically vestigial class of people that have nothing to offer a modern economy. And that class will grow as the economy gets more complex. An increase in complexity is indistinguishable from downward mobility.

Poor immigrants come from places where the cognitive sorting hasn't happened yet.