The NT kernel (used in NT 3.1 through 2000, XP, and eventually backported to Windows 10/11's WSL) was designed from scratch in 1993 with a POSIX subsystem from day one. The whole design philosophy was "multiple personalities" - handle syscalls from different environments by translating them to native NT kernel calls. WSL1 in 2016 essentially reimplemented that same trick for Linux.

Windows 9x, by contrast, was DOS-derived. Running Linux inside it would require fundamentally different (and messier) hacks - which is probably why nobody did it at the time. The very fact that this works at all is a testament to how ahead-of-its-time NT's architecture was.

For a practical answer: you'd need something like this for legacy locked-in situations. Old medical or industrial software that only runs on Windows 98, or specialized hardware without modern drivers. That said, if you have a 486 handy in 2026, running Linux natively is almost certainly more useful than running it inside a 30-year-old DOS derivative.