it was about beating OS/2.
Most of the other UNIX’s weren’t designed to run on 80x86 platforms, so they were never in any real contention with Microsoft. AIX, HPUX, Solaris, Dynix (which was Intel based but had a special architecture separate from PCs) — none of these were in the same market as Windows.
No, Microsoft’s target was OS/2 — which had a bigger resource footprint, but was also a vastly superior OS, with real pre-emptive multitasking, a (by 90’s standards) modern high performance file system, the ability to pre-emptively multitask Windows 3.x and DOS apps well before Windows 95, and a superiors desktop environment (a modern Workplace Shell would still absolutely slay). It was here that Microsoft introduced Win32s and kept changing it every few weeks to break OS/2 compatibility for newer Windows apps. It was here that the per-processor agreements were put into place with systems manufacturers to make selling OS/2 on systems more expensive (for those too young to know, in these agreements the manufacturer paid and charged for a Windows license with every system sold — even if it didn’t come with Windows. So if you wanted an OS/2 system you were paying for both OS/2 and a Windows license you didn’t actually get).
UNIX wasn’t even on Microsoft’s radar in the 90’s — it just wasn’t a PC operating system, and was mostly targeted to systems that didn’t compete with Microsoft. If you wanted a UNIX system, you had to buy your hardware from your OS vendor (much like with macOS today) — virtually nobody (except some of the early cool kids running Linux and *BSD) was buying white-box Intel systems and running UNIX — the numbers were too small for Microsoft to care. OS/2 was their real target — and in the end, it worked.
Yaz