Those 2019 Mac Pros are never going to go down that low.
- They're forever going to be the fastest Intel Macs, which makes them highly desirable.
- The Mac Pro simply does not sell at volume anymore, unlike the Power Mac G4 which did sell quite well to regular consumers. So they're quite rare.
- Everybody in the market for a Mac Pro knew the Apple Silicon transition was right around the corner, so they probably sold even less than we think. Even rarer.
- The iMac Pro had been out for a little while when those came out. Most people who needed Pro hardware had probably bought an iMac Pro. Even rarer still.
No joke, I wouldn't be surprised if Apple sold less than half a million of those 2019 Intel Mac Pros.