I really doubt an average Joe would buy a new computer once the old OS goes end-of-life. Joe would just continue using an EOL system and hope everything is alright.
Software updates will stop and render the possibility of an unsafe system more and more over time. Since there are no updates, if a backdoor is found it won't be patched.
Besides that you'll probably be able to use it for a few more years as long as your apps still work
Having worked in tech fields, legacy devices as old as 20 years can pop up occasionally, functioning or not. Once was told a story where this tech was hired to fix a highschool bell system and the whole thing was running on windows 98. This took place in 2015 or so
I work in a field that is considered by many high tech. I have personally seen a system in use today that duel boots windows 2000 and windows 98.
The product it's used by is old generations and the system does not have any network access but still must be supported by government regulation for several more years....
Few years ago there was a story in a local paper about building automation systems running on Commadore 64 and still doing fine. Build by some company in the 80's. They weren't online, so no security issues.
Tried to find the article online but no luck. It would have been in local language anyway.
In this case I do partially agree with it. They are for medical implants and since the expected lifetime of the device is 10 years we need to be able to support them for 10 years after the last surgery.
If the dog eats your controller which allows you to turn on and off your device we need to be able to sell you a new controller and NOT tell you "sorry, you need to spend several hundreds of thousands of dollars in medical bills to replace the device and go through a traumatic surgery to install it"
Now optimally my company would make a modern program that duplicates the technology but is compatible with modern computers but since are no longer making money on these old devices they don't want to invest the time and money. So yeah..
The company I work for has no control over the air conditioning in one of our facilities because it's automated and running on a computer system from the 80's. No one knows how it works.
It's my ass to freeze, not to pay for. I can switch between uncomfortably hot or cold; I just have to switch a lever (on top of the roof of the building) but I'm not really a heights kind of person.
I still do monthly service checks to industrial computers that use win3.11, 2000 and unix from early 90's. When machines that costs even up to million to replace require legacy os, you scrounge up older hardware to run them as long as you can.