How come? Here in UK you just remortgage for the remaining term of your mortgage, if you have 14 years left you just remortgage for 14 years. Is that something that you have to to do in America, or just what most people choose to do?
There is generally no prepayment penalty here, so if you want some length that isn't one of the standard ones you can just get a longer one and then pay some extra principle each month to pay it off over the timeframe you wanted.
All you're doing is taking out another loan and using that loan to pay off the original loan. So whatever terms you can get from the bank are fair game.
Also, there's nothing stopping you from paying the loan off early.
There are other government regulations and subsidies that encourages and compensates lenders for participating in this market. The government gives access to low interest loans through the federal reserve banking system, created private entities (such as Freddie Mae) that purchase conforming mortgage back securities and requires buyers to pay for loan default insurance until they have a specific amount of equity in the home (which compensates the lender in the event of a foreclosure).
These policies and subsidies are the only reason this market exists and is able to be so highly beneficial for buyers and allow for such a long-term risk taking.