If we're trading anecdotes about a really specific subset of users here, I know a bunch of "retired people" who also almost exclusively do email, but you know they also like things to be easy, intuitive, familiar, functional and still kind of pretty like they're actually part of the future. They absolutely can not have it break. And you know what? They do want more features that they can use, it isn't that they only want email because it is all they can use, it's just the rest is not easy/intuitive/familiar or is providing no greater value to their now limited time. What value does linux desktop bring to them? It's a liability with no advantages.
So now a bunch have started using things like amazon photos which has encouraged them to become more interested in their android devices, branching out into other fun photo apps and home IoT crap. Another bunch (quite the dividing line here) has gotten more involved in iCloud shared albums and thus again more interested in the Apple ecosystem. They went from cheap "PC" buyers to MBP because they thought the UX was that much better, because facetime and iMessage and other cool things.
Linux Desktop can't compete even in that easiest of user segments.
So now a bunch have started using things like amazon photos which has encouraged them to become more interested in their android devices, branching out into other fun photo apps and home IoT crap. Another bunch (quite the dividing line here) has gotten more involved in iCloud shared albums and thus again more interested in the Apple ecosystem. They went from cheap "PC" buyers to MBP because they thought the UX was that much better, because facetime and iMessage and other cool things.
Linux Desktop can't compete even in that easiest of user segments.