the interest rate is a very complicated issue. it reflect the expectation of inflation, economy and other things. the simple explanation to your matter is:

bank do not think inflation will be an issue. short term they do see it may go up. but not long term. so give you long term high rate, expose them to high risk. that;s why 6 month rate is highest.

short term interest and long term interest are 2 different things. my explanation is not accurate, but i do not know another easy explanation without sounding 2 academic and useless.