If housing prices drop and a crisis ensues, government/central banks lower interest rates and provide stimulus in the form of grants/loans/monetary expansion to prop them up. It becomes clear that the only way to make housing affordable is for authorities to have the political courage to let a crash happen.

Its just that never before has there been an investment firm large enough to take a big enough share of the largest market in the world, the US housing market.

They didn't take a large share of US housing, they took a large share of available housing. Several orders of magnitude difference.