I say no on McCabe flipped, but yes on there are bigger fish to fry.
This looks like a move to check the emerging Dem narrative that Barr is Trump’s toady. I tentatively file this under prepping the battlefield for bigger stuff to come.
It reminds me of when the DOJ declined to go after Comey for his leaks. The reason given was pretty explicit: we don’t want to look petty or vindictive.
Remember, you only have ONE opening salvo. Do you use it on McCabe? Or do you save it up for better effect later.