Maybe. Just plain politics is more likely. Decommissioning projects like this very likely touches upon various politicians' pork projects who don't want those to go away. The military brass tried to stop the production of the M1A1 once because they had better tanks, and wanted to buy those instead, but Congress didn't because too many of their districts relied on its production.

No that's incorrect. Decisions on programs the size of the B-21 are made by the USAF Chief of Staff, senior members of the Congressional Armed Services committees, and ultimately by the President. Those people are cleared for everything related to procurement. They couldn't do their jobs otherwise.