Everyone knows OS and software, browsers, etc all use way more RAM than they used to, and arguably more than they rightfully should. Bloatware, etc.
I saw something recently that alleged MS puts a lot of shit into PCs that say they are doing one thing but are really doing another.
It would be wild if they are basically using the PCs of the world to do something like crunch numbers, mine bitcoin, etc. Oh, hey, this guy has 12 gigs of ram and is only "using" 4, that's 8 for us to sap.
If that was the case then there wouldn't be botnets.
Yes, there are botnets, mostly on the PCs of people who are clueless about how anything works.
If Microsoft tried anything like that out-of-the-box, at least one or two of their hundreds of millions of users might notice it and say something.