Are they suggesting that Windows 11 is such a resource hog that anything older than their allowed CPUs will run so slow that it will make their OS look bad??
That's exactly what they're saying. Running Windows on an older machine will make it look bad, and they don't want that.
Not that it really matters, but it's not really what this says.
Even Windows 11 would work perfectly fine with CPUs from 10 years ago. Moore's law for CPUs has clearly slowed down significantly. And the resources Win 11 would use more than with older versions would essentially be related to all the telemetry and online accounts crap. Win 10's (and 11 is probably very close) kernel itself is actually not bad and all in all more efficient than previous versions. The GUI, well it's not all that fancy either. With any reasonable grahics card, it should be plenty.
Now there can be reasons for stopping the support of older hardware, even if it's perfectly fit performance-wise. First, to cut development costs: the more hardware you have to support, the more maintenance and testing you have to do. It can get extremely expensive over the years.
Of course, another reason, as many can guess, would be purely commercial: by pushing sales of new hardware, they give incentives for hardware makers to buy OEM licenses, because it gives them a good reason to sell to their customers for buying new machines.