Most people don't have the financial wisdom to judge "too good to be true" on a macroeconomics basis. Specially not before the bubble burst, when even most experts regular people had access to thought there was nothing wrong with it. Someone offered them a great deal and they took it, simple as that. If a bank offers me a loan with very low interests should I consider the state of the whole economy and the impact of my loan on the country in 10 years before I take it?

Compounding to that the fact that these people weren't even benefited by the whole scam. They lost their houses, their savings, everything. If they knew what was at stake they might bear some responsibility, but they didn't.