The first Microsoft OS was a UNIX variant called Xenix "The first operating system publicly released by the company was a variant of Unix announced on August 25, 1980. Acquired from AT&T through a distribution license, Microsoft dubbed it Xenix": https://en.wikipedia.org/wiki/History_of_Microsoft
Windows NT only got the bare minimum POSIX support for Windows NT to be allowed into DoD contracts. It was barely improved from there, and its SUA replacement was hardly any better.
Mostly ignored by Windows developers and finally put to sleep in 2003.
Xenix, which was actually my first UNIX experience, predates Windows 3.x success, and was largely ignored as Microsoft decided to focus on MS-DOS and OS/2.
WSL exists, because Microsoft realised plenty of people don't care about Linux, and rather buy Apple hardware for a POSIX experience, and since Linux kernel ABI matters more than POSIX in modern times, so WSL it is.
One needs to sell that Linux Desktop experience, that is taking decades to move percentiles.
None of that is relevant for Windows developers targeting Win32, and .NET technologies, the crown jewels.
Need to? No. Microsoft seems to think the UNIX culture is very important to them and to their products and WSL has achieved wide success:
https://learn.microsoft.com/en-us/windows/wsl/about#:~:text=....
There was "Microsoft POSIX Subsystem" https://en.wikipedia.org/wiki/Windows_Subsystem_for_Linux
There was "https://en.wikipedia.org/wiki/Interix"
The first Microsoft OS was a UNIX variant called Xenix "The first operating system publicly released by the company was a variant of Unix announced on August 25, 1980. Acquired from AT&T through a distribution license, Microsoft dubbed it Xenix": https://en.wikipedia.org/wiki/History_of_Microsoft