Understand that Microsoft’s development of Windows 11 was around security. They’re putting their money where their mouth is on security implementations by designing their next-gen products with security built-in.
The processors not supported by Win11 are those known to be subject to the speculative execution and side channel caching exploits. These are not minor flaws, and while Windows 10 was patched to prevent exploitation, they’re admitting that it’s only a matter of time for those to be compromised. In lieu of continuing to patch Windows 10 to death for that specific exploit, they released Windows 11 to only support the newer processors.
Additionally, they’re requiring UEFI BIOS and TPMs in Windows 11 machines. These are much more secure functionalities in mainboards and go toward keeping that OS secure. TPMs especially offer cryptographic localization to help with disk encryption and certificate management. These new features will usher in a new way of maintaining security and integrity in the world of computing.
The secure platform might be a problem for many PCs, UEFI less so.
That is partially true, but not completely. The processor in my primary laptop is an AMD Ryzen 5 2500u with a 25 watt TDP. It did not make the list, yet it has all the public announced required security enhancements. It runs Windows 11 with no problems but there was a bug affecting the performance of AMD processors when the list came out.
Currently it is very easy to run a noncompliant computer on Windows 11.