Sounds like a large part of your issue isn't related to your end question.
You have a bad dealer for support. Unfortunately that's not uncommon. But there are a fair amount of people who did what you said and got the update from their dealer. So most of that problem is with your dealer...
As for your question on consumer updates, car manufacturers are pretty slow in that area..
Not totally dead, but slow..
Of course, there is Tesla with their OTAs..
Also, I know my wife's Jeep, I can download an update from the web and install it myself for the stereo..
(Although that's a bit safer as the stereo in the Jeep has nothing to do with the car.. The Bolt, the stereo is tied in to other car features also..)
So there are some where you can do that...
(And you can do that with the Bolt, but that's in other threads and not something I think GM is advertising..
I think GM will get there (the fact that the stereo has an option for updates is promising), but they are just being extra cautious..