Earlier quoted context omitted.
Because as the sibling comments point out, the price of a Mac Pro isn't just an "Apple Tax^WPremium" over a desktop machine but is an order of magnitude more expensive (assuming you don't care about workstation-class components, i.e. Xeon Ws, Radeon Pro GPUs and ECC RAM). There's an enormous price gap between a Mac Mini and the Mac Pro (especially when the Mini now has higher single-threaded performance than the base…
I've had a continuous string of Mac Pros from G3 to 2012 (MacPro 5,1) my main workhorse. I have continually updated and expanded it. The 2013 mac pro was a mess. pass. The latest mac pro... I think it wasn't just expensive, it was sort of sucker expensive.
It's the kind of Mac that makes you get an iMac to put on your desk and a beefy Linux server-grade box you hide somewhere, but that does all your heavy lifting.