[krzyk]

Or why are other packages patched? Is it because it takes long to accept them at upstream?

But why is kernel is patched by distros at all? I run kernel from kernel.org always and don't see any issues.

[zaarn]

On arch, patches are usually done to either customize the build version (the kernel is 5.9.xy-arch1 for example, that's the only patch), or to make them build with the newer compiler and libs present on the system. Additionally any patches necessary to make them work at all, though in my experience rare.