It would be terrifying for any bank to give people 30 thirty year loans at historically low interest rates (because of the interest rate risk - rates have nowhere to go but up, and the bank could easily be upside down for most of the loan), so the U.S. government subsidizes/backs most mortgages (fannie and freddie). This tends to increase the cost of housing while taxpayers are taking on the interest rate risk instead of the banks.

The U.S. is an anomaly with these loans. Most countries don't do this 30 year fixed low rate mortgages like the U.S. It simply doesn't make sense for lenders to underwrite long loans at low rates.