Operational necessity precludes grounding the entire fleet.
Simple enough.
Even if they found something of interest/concern fleet-wide....they would have to do a phased program of inspections all the while meeting Operational requirements.
The Air Force could alter some demand by altering the way they operate but Combat Operations would have to continue even at some risk if need be.
The Tankers are not hauling blue collar folk on sunshine holidays....they have a mission that requires they be there to pass gas.