I had no idea there were that many W7 machines out there!
I’d guess the bulk of them are POS systems. I’ll poke around a bit.
I have a hunch most of them are contented business people and private individuals. Certainly Win7 replaced XP in a lot of POS type applications, but most of the remaining XP machines are those POS and ATM installations.
Win7 is the best OS Microsoft ever produced, and IMO, ever will produce. Win8 was a disaster, and Win10 is a moderate recovery from that disaster. I don't think they'll ever get back to the simplicity of use and functionality of Win7 again, the way they're going.
That's just my opinion, but I know it's shared by many.
Please do comment again when you've done some digging. I'm quite curious as to what you find out.