Re: And they say Win10 is stable?
Because Businesses run on Word, Excel and PowerPoint. There are Linux, Mac and even Android versions, sure, but the apps will probably be the best on Windows.
If it's used in the office, it's less difficult to just use it at home because in general, it "just works". Anything a regular user needs to do is covered and if they need to find a setting, they need only Google it and have the best chance of finding an answer due to the huge install base.
Because people use it at home, the most applications, in the widest range are available, including games, which are one of the main use-cases of home PCs.
The Windows ecosystem is self-perpetuating at this stage. The only way for it to stop self-perpetuating would be for MS to stop existing so that new PCs weren't sold with Windows and new computers would be sold with another OS by necessity.