Apple didn't raise the price as much as they raised the base configuration sizing. The 2019 MP came with lower minimum on both RAM, SSD , and GPU . Apple isn't going to give away more of those for free. Paying more because are getting more.
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Video Options: 580X vs 60 core GPU
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Compares all differences between the 2019 Mac Pro and the 2023 Mac Pro towers. Specs, expansion and more.
everymac.com
The GPU in 2023 model is closer to W5700 than a 580X ( which was dated at the MP 2019 release and just got 'older' over time. ).
For perspective, the base version 2013 MP came with a 256GB SSD 9 years earlier.
Technical specifications for the Mac Pro "Quad Core" 3.7 (Late 2013). Dates sold, processor type, memory info, hard drive details, price and more.
everymac.com
The 2017 iMac Pro base SSD configuration was 1TB. So 2 years later going backwards in capacity. Apple already knew most users were going to pick 1TB (or larger) as a starting point.
That base SSD configuration was likely aimed at folks who either didn't like or wouldn't primarily use the SSD. ( either using MP to run a hypervisor and real user OS is stored elsewhere. Or just use the SSD to core maintenance but day-to-day OS stored elsewhere. ). The MP 2023 just goes to the standard size that most folks who wanted to substantively use the SSD selected in BTO. Similar with GPU option. Apple trying to cover the W5700 zone ; not the 580X one.
If you put the MP 2019 BTO page into 64 RAM range, 1TB SSD range , and W5700 there wasn't a price increase. If folks mostly bought that before , there wouldn't be much of a volume drop on common configurations as bought from Apple.
There was a 100% base price increase from MP 2013 to MP 2019 but that was all on Intel. There is nothing material the M-series brought to that aspect. Apple was OK with shrinking the target market before they go to 2020.
Folks can grumble at the configuration up from the base configuration. Buying 3rd party RAM versus buying Apple BTO RAM isn't an option anymore , but already at the base price.