MacOS versions tend to receive security updates for 2 additional years after they’re supplanted, so it’s more like 7-8 years. Plus, all of the Macs that aren’t eligible for Ventura can use Bootcamp to install Windows or dual boot into Linux if you’re not happy with MacOS anymore.
The newest machine that can't run the new version would be a Mac Pro purchased a scant 4 years ago. Potentially for several thousand dollars.
Meanwhile there are 10 year old ~$1000 Thinkpads running Windows 11 or Linux. If they just wanted to run Linux on it they could have saved themselves some money.
8 years of updates to current version and 10 years of security updates should be the absolute minimum for every expensive hardware.
I question anyone purchasing a machine with generations old hardware in 2018. Especially considering the Mac pro had been supplanted by newer macs at that point.
It's not really about the CPU power, more that by 2018 it was well known that the Trashcan Mac Pro was a dead-end design and a soon to have radical refresh.
