Do you think Windows OS is a profit center, especially after factoring in the cost of security fixes for older less secure releases? I'm guessing not (I don't have the figures) and Microsoft would rather you replace your 10 year old laptop that can't run Windows 11 or run Linux on it. They really don't care which, just as long as you go away and they don't have to support you anymore.
I'm not assosciated with Microsoft, just someone who has been using their products for 40 years. I am someone who can read in between the lines, and this is my take.
The consumer editions are not all there is to Windows. Nearly every seat of Windows 11 Enterprise used in corporations is a paid license and there are a lot of corporations. Nearly every instance of Windows Server is a very expensive paid license and is required to run Active Directory, MS Exchange, SQL Server, etc.
There are a lot of Steam gamers with 5 games in their library who log on once a month. There are a few Steam gamers with 5000 games in their library who are permanently logged in. There's folks who play one game obsessively, and folks who tinker around with many games.
I'm willing to bet that the 3% are the kind of people who buy a lot of games.
I'd love to see that "what percentage of games have been bought by people on which platform?" metric. I think it'd be a lot more than 3% on Linux, even if you count Steam Deck as a separate platform.