The thing that made Microsoft the de facto computing platform for several generations was the sheer laziness of IBM. Basically nothing about the model 5150 PC was proprietary to IBM; it used lots of off the shelf components, and they even arranged a non-exclusive license for DOS from Microsoft. The only thing IBM actually owned any intellectual rights to was the BIOS, and the minute Compaq made a compatible but non-infringing BIOS it suddenly became not IBM's platform, it was Microsoft's platform. No other system at the time did that especially in the reach of small businesses and ordinary citizens; the closest was CP/M which still required machine specific versions of the OS, software, even data disk formats weren't interchangeable.

That led to mass adoption, then "This new Windows computer can still run your DOS software" followed shortly by "AOL Keyword TRENDY" and look where it got us.