According to Microsoft's security director, it's ARBITRARY.

https://twitter.com/dwizzzleMSFT/status/1408539533465985024

"Seems like you are assuming there is a specific security feature that defines 8th gen as the CPU floor. The floor is set for a range of quality, performance, support, and reliability reasons to ensure a great experience."

If there's going to be a cutoff based on performance, having it almost unconnected to actual performance is pretty exasperating.

That sounds quite unreasonable. "You don't deserve to "experience" Windows 11, unless you can afford the newest computers. And if you can't, we won't let you have it. Because maybe it won't work perfectly. Even though you got your computer 4 years ago."

What else other than Intel’s marketing materials use “xth gen” notation? That itself suggests it’s a marketing ploy.

Oof. I'm starting to think there's a bit of old Intel CPU stock they want to make unsaleable.

When they decide they don't want you as a customer any more woudn't you prefer it to be arbitrary rather than targeted specifically in your direction?

Especially considering that there are plenty of slower clocked Celerons on the list.

Not true. 7th gen gained Mode Based Execution Control which greatly decreases the overhead of VBS. 7th gen also gained SMM Security Mitigations 1.0 and some UEFI hardening.