And what were the whites fleeing?
And that was bad why? What's so great about being around white people?
Mandatory busing of school children. I take it you weren't around at the time.
The US government, in its infinite wisdom, decided that everywhere the black/white ratio of students didn't meet the proper number, white school children would be bussed away from their neighborhood schools to schools where there weren't enough white children. Many children who lived within walking distance of their neighborhood school were bussed, sometimes for an hour each way, to different schools. The only solution was to move to a different school system in the suburbs.
The statement that the "government subsidized" this is a lie. In most cases, the houses became worthless as everyone else was leaving, too, so the housed were abandoned. In Detroit, two of every three houses were abandoned. The owners got nothing.