I think the root of the problem is mostly that the computing industry as a whole has settled on neither the degree to which Unicode should be preferred over ASCII, nor the best way to input Unicode characters. For user-facing stuff, you can at least usually spell your name correctly in text fields such as the one I’m typing this post in now. Support is inconsistent, though, especially when it comes to how Unicode is displayed. It’s pretty easy to find àçëñtėd characters in iOS and macOS (at least if you have key repeats turned off), but there’s no real cross-platform standard for it — no “QWERTY, but for special characters” layout that we can all agree on. And even if there was, do you think the general populace would rather have two different keys for “ and ”, or do you think it more likely that they’d want a single " key and have the OS/editor figure out which one was meant? Fundamentally, our keyboards are inadequate to the task (especially when you consider that there’s so much more to Unicode than just putting accents over otherwise ASCII characters), and neither MS nor Apple has the courage to take the first step WRT updating their keyboard requirements and hardware.
Of course, in the specific case this thread is about, it’d certainly be possible for language maintainers to add support for converting “ and ” to ", but then they’d have to decide whether to do a straight conversion or if they should require matching pairs (is “string“ or ”string" ok, or does it have to be “string” or "string"), and heaven help us if all the major languages don’t agree on which way is correct. I suspect that the language maintainers don’t consider it a big enough problem to worry about. There have been some interesting threads about Unicode over on the Swift evolution forums, but I don’t recall any that specifically deal with smart quotes.
When I was a kid, people who did wrong were punished, restricted, and forbidden. Now, when someone does wrong, all of the rest of us are punished, restricted, and forbidden... and the one who did the wrong is counselled and "understood" and fed ice cream.