They take advantage of pent-up demand to get a higher profit margin for the shiny new things. The price will go down over time after the market has been saturated a bit, when the new Mac Pro has fully taken its place as a regular member of the Mac lineup.
Also, when the new Mac Pro is updated, the cost of the model due for release this Fall should be much more affordable, either through third parties or refurbished from Apple.
EDIT: Missed your most recent post.
And Apple's history of pricing products. I started with used G4 many years ago went to a Hackintosh, then Mac Pro1,1 then 3,1 onto a 5,1 and said see you later to Hackintosh again when the trash can came out. I like the operating system but the over priced hardware and upgrade lockin never again. Windows 10 is more than usable as I have discovered when purchasing new laptop earlier this year. When High Sierra is done with security support it is where I will end up I think. Hell I think if I want I can run a supported MacPro5,1 on it, the irony does not impress me...