They don't like offering short term loans because the returns on their loans are focused around long term mortgages. (hardmoneyfirst.com)
In contrast, long term mortgages often allow buyers to purchase a larger or more expensive house because the amount is spread out over 30 years and the payments are much lower. (mortgagecalculator.biz)
Banks pay more for long term deposits so they have to charge more for longer term mortgage loans. (remonline.com)