Banks don't like to offer 30-year mortages unless someone else is left holding the bag if the homeowner can't pay. That's just too long a period to depend on repayment and market stability. But a 30-year payback period, all other things equal, helps many non-wealthy consumers buy homes. Banks will make 30-year loans if the government, or government-backed entities like Fannie and Freddie, gurantee the loan when a consumer defaults. The president has called for an end to Fannie and Freddie, but, at the same time, he insists that consumers have a 30-year-loan option. Read about it in this article by Zachary Goldfarb.