no one took the initiative, microsoft? AMD? Intel?, back ward compatible is good but too many ancient stuff is no no.
What AMD did was added x64 extension, it helped to extend x86 cpu life
Intel hit the wall with itanium.

honestly who runs ancient stuff on latest shiny cpu with 5GHz 16 cores? nope.
Old software has too many limitation it will not able to utilize all the cpu.

I still have really old game such as heretic and other dos games run perfectly fine either via Steam or inside VirtualBox.
when ancient stuff can be emulated then it should be removed, other wise it will snowballing, old stuff should be left behind, like what AMD and Nvidia did do their old GPU
they only support old GPU up to certain version of OS, or number or years.
why qualcomm elite cpu can emulate x86 cpu while their own powerful x86 cpu couldnt...?
like, who still writing software optimize for MMX? new instructions are much more faster...