They need to know they have the support to fight in the strongest way possible. Dianne Feinstein, for example, has voted in favor of every Trump appointee so far.
I think it's short sighted; the administration is throwing a bunch of grenades up in the air counting on distraction and wearing people out. The reality is the easiest way to have flicked off this booger was the election, and that's over. Dealing with it is much harder, much more expensive. So you have to triage which battles you're going to fight, and how. Don't count on the replacement appointees being any better, and don't count on multiple rejections in a row (it never happens, and not because they become more politically agreeable), because literally there's another important item that will be on the agenda and getting sucked into a cabinet nominee black hole is not a hill worth dying on.