For most users, that's just *way* too hard to do, so it never gets done.
With Windows, it'll force updates on you at some point, so Grandma will be updated whether she wants to or not, even if she's in the middle of something. Users like that *need* this.
That's *way* too hard for many users. If it isn't done completely invisibly in the background, or completely forced on the user, then it just won't get done.
And then there are these ultra dedicated people who do everything to be independent from others to the point of social isolation.
What is happening?!
Still, when Grandma won't update her computer because clicking a few buttons and typing a password is too much work, we can't point to the past here: she wasn't updating computers in her younger years either, and usually wasn't using a computer at all. Even middle-aged people now are using computers and smartphones, when in their younger years they didn't have those things.