That 83% is very shaky at best.
First, number of websites != number of platforms. If you go to the source of the number, they even point out as much:
> WordPress, which is used in more than 30% of sites, includes jQuery by default.
So right off the bat, you're looking at 50% or so, maybe plus a few for people who actually make a point to write jQuery + for wordpress specifically.
Secondly, that study has detection issues [0] that seem to not pick up a good deal of bundlers/etc, which makes it really hard to say how many of React/Vue sites are missed.
Thirdly, jQuery being used as a dependency of a library will still count it in that 83%. They show a few combination options specifically, and show it's at least 1.7% [1]. With others, say 2.5% in total. Think about how many bundlers hide React/Vue and how many common dependencies could use jQuery, and you're probably much higher.
Given all that, I'd bet that number is closer to 17% than 83%, though I'd wager around 33%.
Even with that 33% being jQuery without a framework or not being wordpress, you have to remember this is published. How many of those have had code significantly changed in the past 5 years? This is what's relevant in this context. All of this long winded nuance to say that I don't think "your average jQuery question is probably useful to many more people than your average React one" holds up, at least not like you might think that cited number shows. That's not to say it's irrelevant, just less relevant.
[0] https://github.com/AliasIO/wappalyzer/issues/2450
[1] https://almanac.httparchive.org/en/2020/javascript#framework...