[nonameiguess]

It's not just security. There's incompatible dependencies. Virtualization allows you to run Windows and Linux on the same server, 40 different C libraries with potentially incompatible ABIs, across X time zones and Y locales, and they'll all work.

You can provide the same level of replication and separation of dependencies in an OS, but at a certain point you're just creating the same thing as a hypervisor and calling it an OS and the distinction becomes academic.

[mikewarot]

I think that eventually every OS will converge on the same API, for now there's APE - Actually Portable Executables from the Cosmopolitan C library to get one code base working everywhere without a ton of ifdefs.