Companies that buy 10, 20 or even 50 of the top tier Mac pro's are buying those for the raw power. They aren't going to use them for 10 years, because a) after a couple of years they're depreciated so the company will probably buy new ones for tax reasons and the performance gains. If they don't upgrade after a couple of years, they get 10 years of use with either OS version updates (seven years) or security updates (10 years). They won't complain.
So much this.
Real businesses who purchase computers plan on keeping them 3-5 years because that's the expected usable life for tax purposes, warranty purposes and generally the best bang for buck in terms of when to trade/decommission them for increased productivity.
Whether its 10k, 50k, or 500k computers are not things expected to be cost effective to keep for a decade.
This is not exclusive to macs, but the same for desktop/laptop PCs in enterprise, servers in on-prem environments and cloud hosting providers.
Being stingy and trying to band aid 5-10 year old machines to do real work is false economy, keeping your staff up to date with fast easy to use hardware is what prevents staff turnover (which costs you a LOT more than the cost of the machine) and helps employee productivity (which will generally pay for the machine in a short period of time).
If a new machine would have saved the end user as little as ~2 hours a week in lost time (and seriously, using some old pile of junk i could spend that much time per week swearing at it), that's typically ~5k/yr for someone billing out ~$100/hr.
At that rate, over the 5 years you kept the 10 year old machine too long that's $25k in lost productivity alone, never mind the possible downtime lost due to out of warranty coverage hardware failure.
The cost of these machines, assuming they're used for the jobs they're intended to serve is chicken-feed vs. the billable time for those using them.
If you're a hobbyist, i can see why you might think differently, but the high end pro machines are not aimed at you, they're aimed at people using them to generate revenue.