its all about UX, if you have an environment that has lots of menus and settings something even bios had to control certien aspects of your system like virtuali

its all about UX, if you have an environment that has lots of menus and settings something even bios had to control certien aspects of your system like virtualization support and such you would like to have good UX, because of that UEFI was created. Now if you wanted to do that from OS you can but you need a technology many people hate and want to remove from their systems and hardware called Management Engine. Yes this is the purpose of ME allow changing of UEFI settings from either the OS of machine itself or changing of UEFI settings from another machine without requirement of IPMI(idrac iLo and simular implementations) and rebooting to get to it. Implementation of some sort of ME allows you to overclock your CPU from OS. So AMD has some sort of ME(of course its not called ME since that is just name of intel implementation) as well(how wide in functionality is another question) so do GPUs.