Why can't TempleOS run on modern x86_64 machines?

TempleOS is certainly Intel x86_64, but shy of that there are no guidelines to what machines can run it on the bare metal,

In the FAQ, under "How come it's in the public domain and not GPL?" you can find,

It can run on some bare-metal 64-bit PC's from about 2005-2010 with no layering, libraries, tools, or anything from other sources.

Presumably then there is something about modern x64 bit machines TempleOS can not handle. If so, what are they? What kind of specs does TempleOS require, or what difficulties does it have running on a modern x64 architecture? I know Intel tends to maintain reverse comparability, and I'm not aware of any breaking changes in the architecture.

The README also mentions this, but says it only needs,

  • CD/DVD drive
  • 64-bit
  • 512 megs of ram
  • Manual I/O port addressing

The reason can be found in the TempleOS document Why Not More

I don't stand a chance working on native hardware, anymore. I could install and run natively on hardware from about 2005-2010. It requires BIOS's being nice enough to write USB mode PS/2 legacy keyboard/mouse support. As it turns-out, sometimes the BIOS has PS/2 drivers but purposely disables them, just to be mean. The CIA and whole industry is trying to mess everything up, on purpose. Perhaps, at a point of sale in a store, a thief could hack a credit card machine. Therefore, the BIOS companies actually want it difficult to make drivers and purposely make it broken.

It seems that TempleOS requires PS/2 Emulation for USB devices, or a PS/2 Mouse and Keyboard and that this is what Terry is referring too.