Because employers pay less for labor when the immigrant labor is desperate and doesn't speak the language. V simple. Much fuckery. Need more gallows.

Black markets

Create a bunch of desperate young men that you can easily conscript for military service to do WW3 and write off your debts.

That is why. Today Spain already has more deaths than births (about 320k births vs. 430–460k deaths per year, a natural loss of ~100–130k people annually).  If you remove immigration, you basically see that natural decline directly in the total population. And demographics is very inertial. ...