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

Language is not the problem. The vast majority of immigrants are Spaniards from south and central America. The subsidies are the real problem. The government is buying votes paying subsidies to the unemployed and to ilegal immigrants, mostly Africans, and the jobs are taken by the Spaniards wiling to work for a low wage.

Because nations are ruled by globalist elites that are transitioning away from nation states by dissolving them.

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

Nation states must be dissolved in order to recover our freedoms, but globalist plan is to merge them into larger states ruled by the non elected. Sovereign states will have to be much smaller, highly technological, bitcoin driven communities owning independent territories, ruled by officers selected by merit.

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.