The worst of Xenix was still preferable to the best of Windows.
Microsoft had several opportunities to ubiquitize a quality operating system, irrespective of their horrific business practices. They could have built their next-gen OS on top of Xenix. They could have finished the OS/2 project instead of stabbing IBM in the back and doing Windows on top of DOS. They could have even completed Dave Cutler's vision for Windows NT instead of MAKING THE SAME MISTAKE TWICE and top-loading all of their crap into the Win32 layer instead of building around the NT microkernel.
They could have done any of the above, and still practiced their bullshit monopolistic business practices, and they could have still taken over the market. In fact, if they had built Presentation Manager on top of Xenix, it's entirely possible that Linux would not exist today, and the X Window System would never have evolved past the days of TWM and Athena Widgets because all the unixheads would have happily moved to the commodity operating system.
But no. Aside from being monopolistic bullies in the marketplace, they also consistently deliver really bad products. There is a reason Linux has already overtaken Windows in the enterprise computing market, and has denied them a monopoly in this area. People who run back end data center applications don't want an operating system that has a GUI intertwined with the bottom layers of the OS. They don't want mouse clicks in the same event queue as disk and network I/O. Windows is a bullshit design and it will never be adequate.