They know they'll lose him either way this offseason, and even now they are moving more to Bob, and you cannot blame them considering they are locked into Bob. Driedger will leave because he cannot get a fair shake there, and so a setup of a veteran good goalie in Bobrovsky and a young back up learning the ropes is the best setup they could hope for.
Keeping Driedger for a cup run might be the best option, or a great fallback. But getting an asset might be smart, especially if they are virtually guaranteed to give Bobrovsky the most work going forward.
I like the idea of getting value for an asset thats going to leave, I really do. But in this case I think it does more harm than good. You've got a team thats banged up and fighting for a playoff spot. What kind of message does that send, walking in to the room as the GM saying "Hey guys, I know you're working your nuts off to get us in, so I just traded our stud backup goalie for a pick. Have a good one boys." That ain't going over real well when all they're realistically going to get is a 2nd rd pick. I get maybe not wanting to buy at the deadline, but you can't sell when your team is playing that well.
Theres a lot of 1B UFA goalies available this deadline... Raanta, Ullmark, Rittich, Reimer, Bernier, Dubnyk. And who really is looking to buy? Colorado, Philadelphia, and Toronto. Looks like a buyers market to me