You can’t have it both ways. Either make a proper desktop or don’t. Instead Apple neutered it and act like surprise pikachu when it doesn’t sell well?
1. The Mac Pro is not literally design for a desktop. Deskside maybe, but the rack unit that also came along was a major focus. Rack configurations are not 'desktops'. The Mac Pro 2019 is about as tall as a standard rack is wide; that isn't an accident at all.
2. Apple increased the MP 2019's entry price 100% (from 2012-2013 ) levels. You think they expected them to sell in the exact same numbers? Probably not. The Mac Pro 2019 came with a 'low volume' tax already applied to it. They knew it was going to be lower volume. [ e.g, when selecting 24 and 28 core Xeon processors Apple opted only for the 'M' version that allowed for max RAM but also had an Intel '>1TB' tax on them. Apple just threw their tax on top of that one. It was a higher margin play, not a higher unit volume one. Apple was all too willing to follow Intel into the sky-high Xeon W pricing zone because likely knew they were going to 'exit' x86-64 before that strategy went off the cliff (and AMD undercut and beat them). ]
Very similar issue this time. When Apple introduced the Mac Studio there was a line from MP 2013 --> iMac Pro --> Mac Studio. Studio replaced both the large screen iMac ( pro or not) and also the '$3-5K Mac Pro' used to offer before attaching a screen to it. The relatively higher volume model between the two is the Studio. The Mac Pro 2023 was mainly to catch a smaller set of users at higher margins. ( again the base price crept up. Apple tried to anchor that on the highest MP 2019 configuration sold being 16 core and W5700 ... which was a higher than entry price.
If look at even today's Studio Ultra marketing page the baseline in the performance compare is that highest selling configuration.
"...
Faster render performance in Redshift
5
Mac Studio with M3 Ultra _____ 6.4x
Mac Studio with M2 Ultra _____ 3.2x
Mac Studio with M1 Ultra _____ 2.4x
Mac Pro with 16-core Intel Xeon W and Radeon Pro W5700X (baseline)
..."
The ultimate pro desktop. Powered by M4 Max and M3 Ultra for all-out performance and extensive connectivity. Built for Apple Intelligence.
www.apple.com
The M1 Ultra isn't "clobbering" the 24-core Intel Xeon W with dual W6800 which sold in much smaller numbers; its 'target' is the highest selling configuration. That is extremely likely not an accident; that was likely long term planned while work on the initial Ultra progressed. Some large screen iMac fans took that as the Studio was not a replacement for the iMac. If just switch to the Studio Max benchmarks then can see that is just extremely deep denial. That baseline is an very common iMac 27" model. The Mini Pro and Mac Studio was likely always intended to take out the bulk of the iMac 27" and lower 'half' of the Mac Pro sales. That is Apple intent, not surprise.
Apple was measuring the MP 2019 so several years before the Mac Studio appeared. They probably were extremely likely also measure how many folks bought the Pro VEGA II / W6800 / W6800 Duo / W6900 MPX modules also. ( and how many were buy leveraging the 'free ride' to buy off the shelf 5700 , 6800 , 6900 also). [ Decent chance they knew by 2021 that a very expensive 'Extreme' wouldn't work on projected user base. ]
3. In the 2017 meeting about what didn't work (at the time) for the MP 2013 was issues around
i. one and only one internal drive. I think in part the MP 2023 is around because there was enough doubt they couldn't do a 180 on that one ( in 2019-2020 that was still ringing true and they were selling 'enough' MP 2019 models).
ii. they had leaned on Thunderbolt too much. Likewise in 2019-2021 that was still ringing very true inside Apple.
That 2017 IMac Pro still had all those same constraints when it appeared months later.
A Mini/Studio stack enclosure with TBv5 doesn't increase footprint much and is fast enough for most folks. So Apple could be sliding. backwards on that. Most of "Thunderbolt" has been merged into USB-IF standards process. The "Thunderbolt" branding is Intel based ( who is more then eye-ball deep in trouble. So probably little movement there coming any time soon. )
As long as the MP 2023 is holding a target block of folks on the Mac ecosytem that is probably sufficient for Apple for now.