A sad, ongoing problem, for sure. And not only GM.
I drove by the largest/one of the largest, Chevy dlrs in the SE. He specialized in Vettes and trucks.
His side lot, about the size of a football field, had 2 used heaps on it, awaiting the wholesaler pickup.
His main lot had mostly used vehicles, and not a lot of them. A brand mix that says, "auction stuff".
One of the big hits these new car mfgrs take is refusing to take care of known problems.
The 2014 Silverado LTZ was the biggest pile of junk I've ever owned. $44K worth of it.
It took a hike, and I bought a 2002 Suburban....It "ain't purdy", but at 300K on the clock, hasn't been expensive.