What's driving much of the eligible hardware requirements is to harden security. Cyber-criminals and hackers are exploiting Bios and CPU vulnerabilities that can allow injection and running malicious code, which no software based security can protect against. Thus requiring newer CPU and Bios chip systems.
However, Microsoft is apparently not stopping you from 'manually' upgrading to Windows 11 with older systems. You just can't do so automatically from within Windows 10. Your system won't be as secure if you choose to do so.
Not much different from installing no longer supported Windows 7, Vista, or XP now. Microsoft does not stop you from doing so. Especially, for those running software not compatible with newer Windows versions. Just allowing more pathways open to hackers.