That's similar to saying that Cygwin or MSYS or MinGW or WSL is filling that need on Windows.

The main difference would be in that, since Windows has no native Unix environment, all these tools are added functionality while on the Mac, it overrides built-in functionality and can make things go a bit weird.

Just like it doesn't have a native Win32 environment, rather different personalities built on top of a common layer.

UNIX environment on Windows is just like how IBM and Unisys mainframes deal with it.

Indeed. (Except that "WSL" should be read as "Windows Substitute for Linux.")

I don't remember FreeBSD or illumos calling their syscall compatibility layer for Linux Substitute.

Nor were they called “services for Linux.”

Nor are they called now, rather Subsystem.

I don't care what names marketing departments come up with.

Actually "for Linux" came from the legal department as Linux is a trademark and it's a common practice to indicate relationship with "for X" where X is a trademark (e.g. "Y for Twitter" instead for "Twitter Y" that would suggest close relationship, from the same company).

Thanks for the clarification.

It's more like a "Windows Subsystem for Linux Applications"

The only problem with Cygwin and MSYS and MinGW was that they filled that need poorly.

You could say that WSL is filling that need on Windows now, WSL certainly does remove some of the earlier obstacles/objections why one would want to avoid Windows and use Linux for development.