Escrow account doesn't pay interest

Hello,

I have my mortgage with Washington Mutual along with an Escrow account. During closing I signed all the papers and agreed for an Escrow account also.
But now I came to know that they don't pay interest for balances in the escrow account, so I sent a request to cancel my escrow account so that I can put that money (for property taxes and insurance) in a saving account and earn interest. (the total amount comes to around 9000 dollars). The the banker say that it can not be done.

Aren't they robbing me from my right to earn interest? Is it a fair practice by the bank to reject my request.

Thank You for your response.

NN