Cost of labour replacement.

Its expensive to raise and educate a German child to German standards.

But its cheap to lure in an educated (or at least trained) foreigner with (fake) promises of a better life, and then rely on sunk-cost-fallacy to keep them.

Can you imagine Afghans or Somalis standing for that?

Once the West has attracted a critical mass of people with self-respect and concern for their families, the migration will stop. They may behead a few White leaders in order to implement their preferred policy.

Or when we ruin ourselves completely and become unable to lure foreigners at all.

Whichever happens first, but its surely not sustainable...