Mainly subtle differences around command line tools and the file system. There are UNIX cmdline tools collections for Windows (like busybox) running in the vanilla cmd.exe or Powershell, but they don't quite fit in (for instance the way how string escaping and cmdline argument parsing works). You can use bash in a mingw 'UNIX emulator', but then you can just as well switch to WSL. And those little things propagate and amplify upward into toolchains and workflows.

It's possible to create command line tools that work across Windows and UNIX-oids, and I appreciate this, but it's a lot of additional work (even 'cross-platform' solutions like Python don't fully wrap this stuff, even though they do their best).