> There are clear paths to NOT use anything Microsoft if you want to.
For a lot of people there isn't.
Take my dad for example. He sells weight scales for retail (think butchers, greengrocers, cheese shops, etc). Those scales are pretty much embedded PC's nowadays, they connect to the internet and can be remotely accessed to update product prices, promotions, get the daily sales numbers but also things like changing the logos and text on the receipt and a million other things.
The manufacturers of those scales sell a piece of software to do that, but it's always a 100% Windows app, held together with all kinds of (outdated) MS technology like Visual FoxPro. Often they have licenses that require hardware dongles, have bizarre drivers to communicate with the hardware and it feels like it's al held together with spit and ducktape.
There is no Linux or OSS alternative, the protocols aren't even published and no one cares to reverse engineer them as the market is just tiny, and the target audience has no overlap with the techies that are interested in Linux and the like.
And that's just one example, there are tons of crappy, outdated, proprietary apps like that out there. Apps with tiny user bases no one cares about so no OSS options will ever emerge.