Fixed rate mortgages are loans that have an interest rate and payment that are fixed for the entire life of the loan. You know today exactly what your payment will be 25.3 years from now - the same as today's payment. These are the most conservative loans available given the certainty that they bring, but they come with a small price: the interest rate is higher than for some of the other programs.
The lenders are guessing at what the financial markets will be doing 15 and 30 years from now. As this is a long time off, and the lender does not want to be caught with a loan too far below market rates, the rate is set somewhat higher than for a loan which will allow the lender to reset the interest rate sooner (an adjustable rate mortgage for example). The longer the lender is locked in, the higher the rates.