So we're talking about 5 million machines with an OS designed in the late '90s (20 years ago) and that stopped receiving any meaningful updates 4 years ago.
Most of them are actually ATMs in developing countries like India and they are definitely not air-gapped [1]. The POSReady XP with the bare modicum of support until April 2019 made companies take it as a green light to keep using XP in embedded systems.
Other systems running XP: many of the NHS systems hit by WannaCry last year, many of the systems in UK Police stations, most electronic voting machines and gas stations in the US, most digital signage in train stations, airports, hospitals, or cinemas, parking garage payment machines, so many POSes, even passport security in some airports!
Does this put the magnitude of the problem in perspective? It's a threat from so many perspectives. Your safety, your data, your money, you name it.
[1] https://www.rbi.org.in/scripts/NotificationUser.aspx?Id=1131...
I think you're severely over-estimating the criticality of stuff that's still running XP. It's mostly used for antiquated industrial hardware that gets used 5x a year, maybe (old CNC mills and whatnot), often times with no network. If it gets crypotwalled via flash-drive then someone will reinstall it and carry on with life.