Like Dheer said, the demand for shorter term money is greater than for longer term money, precisely because the banks don't want to have to pay big interest rates for long periods.
Banks borrow short term and lend long term - so they take money from you for one year, and lend it away as a 20 year mortgage. After a year, they take money for another year. Since short term rates tend to be higher than longer term rates, they make money off the "spread" (or the different between the rate they lend and the rate they borrow).
In this scenario, banks should pay higher for longer term deposits, but overall banks realize that interest rates will go up and down, and they don't want to lock the "up" for a longer term. Since banks believe that rates will come down in the 1-2 year period, they offer good rates only till the 1 year period and disincentivize longer term deposits by offering lower rates.
If you look at the interbank or money markets, trading of very short term bulk money shows that for the 10-15 day periods, the interest rates being offered are 10% or so, while for one year it's just 9.5%. The market believes that interest rates will go down in the one year time frame - but you never really know since this is just a bunch of people that believe so.
Eventually, if rates continue to go up, the demand at the longer term will also go up, because it will become obvious that the rate pressure continues to be strong.
If you do want higher rates for the long term, check out State bank of India bonds that are currently trading on the NSE (you can buy them if you have a brokerage account) They are just about as safe as SBI Fixed Deposits, and the rate being offered is around 9.3%, for a 10-15 year term. Hope that helps!