How much would it cost to keep the Hubble in service?
A dedicated Shuttle mission costs several hundred million dollars depending on whose numbers you trust. Add to that the cost of the crew training and the new equipment for the Hubble (not cheap) and the cost for the mission might exceed a billion dollars.
What other programs are you willing to cut to save the Hubble? There's only so much money to go around, so something would have to give. What are you willing to give up?