This demographic shift occurs because we lack cultural borders in the United States. It's "discrimination" now if a Hispanic or Black who rejects civilized values isn't hired, and so they get the job, get the money, and are able to pay for children whites with the same backward values couldn't.
Once they've reproduced to fill a location, they're also able to expand into other neighborhoods as well even though whites with the same values couldn't, because otherwise it'd also be "discrimination".