If it looks like a red herring, and smells like a red herring...
I think the powers that shouldn't be see mass migration as a solution to the problems they created.
Low birth rates -low house prices-shrinking GDP-collapse of fiat based economy.
And they didnt think there would be any trade offs. They assuned people woukd come and either assimilate (because we are so great) or leave (because money is their god).
I dont think it occurred to anyone that people moving here have thier own agency, desire and cultural attitudes.
One day the money printer will stop.
And It's going to get bad.
Historically bad.