Because this is part of a list from Factcheck.org, listing all the things that different people/parties are ALLEGING caused the recession (and decrying the finger pointing, saying there was layered irresponsibility)
I notice that you conveniently left off a number of things from your cut and paste:
--Real estate agents, most of whom work for the sellers rather than the buyers and who earned higher commissions from selling more expensive homes.
--Mortgage brokers, who offered less-credit-worthy home buyers subprime, adjustable rate loans with low initial payments, but exploding interest rates.
--Wall Street firms, who paid too little attention to the quality of the risky loans that they bundled into Mortgage Backed Securities (MBS), and issued bonds using those securities as collateral.
The Bush administration, which failed to provide needed government oversight of the increasingly dicey mortgage-backed securities market.
An obscure accounting rule called mark-to-market, which can have the paradoxical result of making assets be worth less on paper than they are in reality during times of panic.
Collective delusion, or a belief on the part of all parties that home prices would keep rising forever, no matter how high or how fast they had already gone up.