Lacking modularity of the ISA, I can understand why many of those instructions were carried forward.

But all the legacy operating modes too? A modern x86 cpu should only have 2:

# Full-on 64 bit, legacy cruft cleared out as much as possible

# A compatibility mode to run application code written for 32-bit protected mode OSes like Win2k/XP etc

And even that last mode could be optional. Any other legacy support is just waste of transistors imho (however 'few').

Intel made a move in that direction years ago (X86S). Sadly that went nowhere.