The Tevs are probably licking their wounds from the all-out diversionary attack that occured during Delenda Est. Furthermore, they were still in the process of repairing/rearming/resuplying since the Blitz of Darkest Hour. And the Imperieuse, after hiding for so long without proper support, is probably in a more-or-less critical state of disrepair and could probably use that trip to Delta Serpentis she was supposed to do to begin with.
Steele knows the feds are on their last legs, but he wants to finish the war as quickly as possible, so the GTVA can focus on the real threat out there. He'll go for the throat all right, but he'll need a bit more of preparation yet for that.