If you can't arrest the depreciation of a new(ish) vehicle in this market, you never will. As you know, vehicles depreciate immediately, and the steepest decline is the first few years. You won't ever get that back. All you get back, when your negative equity declines, is some of the payments you made as the depreciation curve levels out a bit.
It's a shame that the supply chain shambles don't create a stronger price for our vehicles. But, I'm sure what's happening is that the dealer wants to keep nearly all the margin available. As always, you can do better if you sell privately.