Specter and his team helped Santorum get elected. If he would have turned his back on him no one would have ever helped him again.
You are totally right. If Santorum would have backed Toomey, he would have lost support from the state GOP and the WH. People don't realize how expensive and hard PA is to run state wide. You have 2 major media markets to pay for and lots of small ones in between. Philly alone is murder to pay for.