Because here's what you were able to do back in the day:
"In 2007, Peter Morris applied for three loans from three financial institutions (Washington Mutual, Lehman Brothers, and Bank of America) to purchase three properties, all located at “Sonic Court” in Riverside, California. In the loan applications, Morris claimed securities and assets that he did not own, employment he did not have, and income he did not earn. He falsely stated that he was unmarried, was in the process of selling a different house, and was not obligated to pay child support. He supplied the three banks with false documents to substantiate these false statements. He also withheld information—for example, he did not tell any of the banks that he was applying for loans from the other two. All three banks approved Morris’s loan applications, and Morris purchased the three properties shortly afterward. When Morris made only one mortgage payment, two of the three banks foreclosed on their loans and sold the properties at a loss. Morris sold the remaining property in a short sale, at a loss to the third bank."
Yep. That's what you're able to do when it's totally easy as a Bank to bundle and securitize the loans you make. What the borrower's doing is a crime, of course. But like you care. That's someone else's problem. You're making money at the outset.
Just remember: Capital markets are ruthlessly efficient. No imperfections. No irrationality.