This doesn't appear to have anything directly to do with Linux, just crappy software written by WD running on it. Please be a little more careful with your criticism.
So, yes, essentially you end up with a bunch of devices running vendor-specific unmaintained Linux distros on the wide open Internet. The “unmaintained” part of that sentence is the problem, not the “Linux” part.
Shouldn't we design systems that are hard to break by default? Shouldn't the OS assume that terrible things are going to happen anyway, and provide protection from bad faith actors in case the OS is indeed left unpatched for 10 years while being fully exposed to the internet? Is it even possible to design a system that provides this level of security so that we can get away with near-zero additional security expertise from product designers who build on top of it?
I think that, first of all, it's Western Digital's responsibility that things went south here. But shouldn't we build systems that provide bomb-proof security for the many companies that build on top of it? Is it even possible? And if so, how? In the end we would be doing ourselves (as consumers) a favor.
I highly doubt it, at least not with 100% certainty. We build bridges to last and to stand weather. These are enormous constructions with large safety margins, teams designated just for security (against weather, earthquakes etc) with peoples lives on the line. Yet, we need to inspect them on the regular to make sure no assumption broke, no safety system was triggered and nothing unexpected happened.
If we can't make this work at this scale, I have no hopes that software for comparatively cheap consumer devices manages to achieve this.
However this is a problem the industry has been struggling with for decades. It's simply not easy (and maybe not even possible) to achieve what you claimed "should" happen. Nobody knows how to produce bug-free software at scale.
So if anyone wants to support their 11 year old drive they can do so.
[1] https://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=OpenSSH