You have it backwards. Buyers demanded the ability to buy homes they couldn't afford, the government required Fannie Mae, Freddie Mac and banks to finance them and the US Government guaranteed some of the loans.
The buyer behavior was rational, at least on the surface, because homes almost always appreciate over long periods and were appreciating like crazy during the bubble. We are pattern matching monkeys, all of us, and it's only the few who can see the bigger picture during those times.
Many didn't want to miss out on the big payday buying $300k homes and flipping them for $500k a few years later. All bubbles accelerate bad decisions/behavior and it's really difficult (if not impossible) to legislate incentive driven behavior away. It's obviously possible to not legislate bad market incentives, but we flunked that one to.