What I don't understand is why Microsoft would make Win11 so demanding and practically exclude
people with low end pcs. What is the logic behind it?
Simply put, Windows 11 uses better security features in modern CPU's and motherboards that versions of Windows other than 11 cannot support.
More completely, Windows 11 requires a TPM, which is a cryptographic hardware feature that Windows uses to manage more secure authentication and general security. Windows 11 also requires SecureBoot, which uses the features of UEFI firmware to guarantee the authenticity of the Windows boot files. UEFI is the replacement for MBR and changes the boot process completely, as well as the system disk format (to GPT). Windows 11 also requires CPUs to be able to support MBEC, mode-based execution control, in order to run HVCI, hypervisor code integrity, which helps ensure the integrity of loaded modules (code integrity). You can run HVCI without MBEC, on Windows 10 for example, but the performance hit is large if you do (and that's probably why it seems laggy to you). Windows 11 also uses DCH compliant drivers, this is essentially a packaging technique that makes drivers more secure, this is in addition to all Windows 11 drivers being digitally signed by Microsoft.
All of the above is in the interest of making WIndows more secure and protecting your data and your system from interference from outside. If Microsoft had enabled all these features in Windows 10, the vast majority of PCs would have failed to boot, because the CPUs and motherboards in older PCs don't support these features. That's why Windows 11 is only supported on newer PCs that do contain the necessary hardware.
All that said, it is possible, if you know how, to get Windows 11 to run on very old hardware, but getting it to run is not the same as getting it to run well or efficiently.