BUT OS/2 was originally being built in co-operation with Microsoft just like Macintosh's OS was also with Microsoft.
Microsoft and IBM started the development of OS/2 because IBM wouldn't support Unix. (Microsoft had the most widely used Unix of the day, in Xenix.) IBM required a proprietary OS and had a long-running war with AT&T.
Microsoft backed OS/2 strongly but sales were, in Bill Gates's word, "dismal". It was a flop. However, Windows was a hit.
Microsoft wanted to go to a 32-bit OS/2 v3, which is what became Windows NT.
IBM had sold tons of 16-bit IBM PC/AT machines and insisted on a 16-bit operating system.
Hence the divorce, where Microsoft kept Windows and got a bundle of cash ($25 million, if I remember correctly). IBM got OS/2 and an ultra-sweet deal on Windows ($9 a copy, if memory serves).
However, the Unix business was a huge mess at the time. First, the all vendors were at war with one another, then they divided into two warring camps (SVR4 vs OSF).
While they were busing fighting one another, Microsoft nicked their cheese.....
Update: Of course, Windows NT was designed by the same guy as DEC's VAX VMS, so it's got that in its DNA. Maybe he was thinking of servers as well...