Steam apparently has about 130 million monthly active users and about 70 million daily active users. About half the planet has a computer at home. So, Steam users are somewhere between say 2% and 10% of the world's active PC users.

If someone is a daily active steam user, they spend a lot of time on the computer. If they have to make sure their drivers are up to date and their frame rate is high enough to support their games, they've probably developed a bit of knowledge about the system. My guess is that people who play Steam games tend to be the tech support people for their friends and family more often than not.

So, it's a small group, but it's an influential group. If enough of that group becomes comfortable with SteamOS, they may be comfortable setting it up (or a variant of it) for a friend or family member, even if that friend or family member only uses their computer to watch videos, check emails, etc. In a world where Windows was free and just worked, that might not happen. But, in this world Windows 10 is about to lose support, and Microsoft is suggesting that if your computer can't run Windows 11 you should just throw it away and upgrade. In that world, more people might end up switching to Linux.