There are plenty of white teenagers who work at every In-N-Out I've ever been to--because they pay better. Otherwise those kids, in nicer areas like you point to, have better alternatives for minimum wage like retail. The reason the jobs you describe are being replaced by immigrants is because the wages have been stagnant or not kept up with inflation. Unskilled immigrants take labor jobs that Americans aren't really willing to do, like being a janitor or emptying septic tanks or pouring concrete in Bakersfield.