Because America, by large, has been built upon immigrants coming over and shutting the door behind them so others can’t get their success.

We’ve done it as English colonists, we’ve done it during the Industrial Revolution, we’ve done it in the early 1900s, and we’re doing it now. It’s sadly a trend that we, as a country, never grew out of.

It's a ridiculous process to get a work visa even for skilled and educated people with money. I had a gf who had a PhD in material science with a wealthy family. She was working at a National Lab and was worried if she didn't get a permanent position there, she'd be scrambling to find a job that would give her an extension or she'd have to move back to Europe.

Apparently it used to be easier to get seasonal work permits for Mexicans wishing to work in the US, and it was common for workers to go back to Mexico after the work season. Most did not want to permanently move to the US, but preferred to return to stay with their families. Those visas were curtailed under Reagan, so they became much harder to obtain. Crossing back to Mexico became harder, so now more just cross the border and then never return. If we still had a reasonable system in place to allow temporary workers in, I’m sure we’d see less illegal crossings.