On the flip side, it's the only offering from Apple that offers what everyone else does. Nobody is complaining that Apple offers a $6K tower. They're complaining that Apple doesn't offer any towers less than $6K.
I could put a Mac Mini on my desk with half a dozen adapters sticking out of it, but even then I still can't upgrade the RAM. The last Mac Mini with user-upgradeable RAM was 2012.
The 2019 Mac Pro feels to me like an Apple Lisa. Even at 1/4 the price, it would seem steep to me. I want what it has, but there's no way I'll ever be able to justify that.
This is new territory for OSX-era Apple. It didn't used to be so expensive to buy an expandable Mac. You could get a PowerMac G5 for $1800, and a PowerMac G4 from $1500.