Why only Windows?
What all the software around, for example my ADSL router firmware has not being not getting updates for a really long time. Isn't it a "critical piece" too? (there's now a pfSense behind it, so not much of an issue, in my case).
And the real issue is: how long a company, *any* company, should support its software? Support has costs, and they will be of course charged to users, old and new. What's wrong in charging for support? Don't we pay for maintenance of cars, heating systems, etc.? Why software should be different? Most physical items have a limited warranty (and someone outside EU complains the two year mandatory warranty is too long...). Only life-threatening issue will be fixed outside of it for free, usually.
Software doesn't wear out, but surely "hidden" issues and vulnerabilities may surface. It may not work with newer devices. Old TVs were obsoleted by digital television - should Sony, Samsung & C. have upgrade their TV sets for free? (using an external topbox is no different than putting a damned firewall to protect your old device).
Also, bugs that are critical security vulnerabilities won't cause a system malfunctioning until it's attacked. In some ways, they are different from a defect that will cause issues anyway (i.e. the Intel Atom one). When people talk about cars recall, they speak about the latter. Not a thief bypassing a vulnerable car security system and killing someone while running away. If a ransomware blocks a critical system, the culprit is the ransomware writer, or the OS provider? If you kill someone because you didn't maintain your brakes - even if there are no more spare parts available, who is responsible?
Sure, they are a risk, sometimes a big one. Still we have a lot of intrinsically risky items around (guns, knives, tools, some chemicals), and believe we should manage them properly. We know software has intrinsic risks. Why we shouldn't manage them? If I drive a vintage car or bike, I perfectly know it's far from being safe as a modern one. Should I expect it to be different, and the maker upgrade it for free, in secula seculorum?
In this case, did Microsoft aimed Windows at health devices, promising longer and free support cycles than those for generic use? Or it was the device makers who chose Windows? Why they should be exempt in delivering upgrades of their software running on newer hardware (maybe your ISA card can't work in a modern PC?) and software?
In this instance, blaming MS looks really overkill to me. Sure, it had the patch for paying customers, and probably it has many others. It's how custom support works.