The 30-year fixed-rate mortgage ultimately requires taxpayers to bear the tail risk because Wall Street has proven it cannot absorb extreme tail risk—especially on the house-price side, where firms ran to the government when prices fell; Wall Street's preferred outcome is to revive a 1970s-style Freddie Mac that is purely a government guarantor of default risk (with no private shareholders or portfolio), leaving Wall Street free to securitize and profit from the prepayment option.