I agree with you on this, but I think it likely stems from a couple things, first, people just don't like small D. You have to be pretty special to be a small D in this league and get respect. Second, I think with Chabot and Sanderson on the left side, people don't see a fit for Brannstrom long term. That really leaves us with two options, move him early when he still has value based on "potential", or hope that he realizes that potential before getting pushed down the lineup and losing his spot.
People just saw Logan Brown go from one of our top prospects to traded for a bag of pucks in a pretty short span (3rd on HFSens in 2019, 4th 2020, 11th to gone in 2021), so the fear is that when we finally do decide to move on from Brannstrom, the key piece we got back for Stone will become a 4rd round pick or something. Can't remember where I read it (or heard it) but somebody asked other teams scouts before the deadline what kind of value they thought a guy like Brannstrom had and the responses they got were not encouraging. That was prior to him getting a lot of usage this year, so maybe with more exposure things have changed, but that's likely part of where the rush comes from,
It's a bit like people wanting to move Tierney back in 2019-20. No long term fit, lets move him for a late first or 2nd even though we don't have guys quite ready to step in and take over his role. Instead we hung on and his value has tanked. Right about now, we probably would have been better moving him, but it's hindsight, even a broken clock is right twice a day.