About Linux: is not switching to a new version an update in itself? Maybe your remark would be more correct saying: "older versions don't get fixes". In this case as I said maybe there is enough market, or maybe you have enough money to pay someone to do the job.
The problem are proprietary systems that remain closed when going out of business. It's great when at least some of them close but say "here is the code just in case someone wants it, for us it no longer makes monetary sense"
Example: my Korg Kronos is a synthesizer workstation that runs an outdated Linux kernel on an obsolete motherboard. But it just works, it's a musical instrument so why would it need new updates? Security could be arguable (it even has an FTP server, so, yes, but it's a musical keyboard not a server) New features? The product feature set was closed when I bought it. There have been a few updates but basically everything is the same.
For how long? Day ? Two? Or may be a week? If so they should say it will work for one week. Otherwise I do not see a reason why it should stop working.
If it stops working it's a fraud isn't it?
For instance. I have bought iPhone4. Youtube app doesn't work there anymore but all links are redirected to it so basically you cannot see it at all in Safari. Weather doesn't work there anymore. Safari doesn't open many sites anymore. XCode doesn't support it anymore so I couldn't even put my own software there. Transfer of photos to a M1 Mac didn't work last time I've checked.
Why it should stop working? They should fix it, no? Or at least provide source code so I could fix it if they do not want to.
And this also rises the question of having full access to a device you own, also because those who sell it to you have a tendency to write a garbage software anyway.