Embedded control machines connected to the internet
They shouldn't be, but we all know some are. And don't blame this on an "incompetent IT department" - we're talking about SMALL BUSINESSES here. If you're a small business owner of a tool and die shop with a couple of CNC machines and a half dozen employees, you don't have an IT department. Either you, or your most PC literate employee, is going to be your "IT person". Anything they can't solve you call the vendor of your CNC machines.
It might not be good practice to allow the PCs connected to those CNC machines to access the internet, but many probably are for convenience, in case the operator needs to look up specs on something, email suppliers, etc. Your "IT department" is not going to understand the risks of doing this. If those PCs get updated to Windows 10 but the control function for the CNC machine breaks, you are out of business until the problem can be rectified. Which would require calling up the vendor of those CNC machines and paying a tech $250/hr for a site visit which might require a full day or more to reinstall/reconfigure everything as before and falling a day behind on all your work as a result.
If a lot of that CNC vendor's customers have been hit by undesired Windows 10 upgrades, by the time you call you might get told "we're booked solid for the next six weeks". So you either layoff your operators in the meantime or pay them for doing nothing, and hope you can survive six weeks without any revenue. Even if you can make it six weeks, your angry customers who have to go to someone else to get the work done you promised you could do before their deadline may not be back, so even if you survive in the short run you probably don't survive in the long run.
It would only take a few stories like that which end up in the small business owner going bankrupt and the employees losing their jobs with the blame being put on Microsoft before they'd start to really feel the heat. Doesn't matter if they can be successfully sued, they have great lawyers so they'd win anyway. But all the people sharing this on Facebook would cost Microsoft's brand and image a lot more than any successful lawsuit every could.