It's been a while since I have done web dev, but web devs back then were certainly not scared of any language. Web devs are like the ultimate polyglots. Or at least they were. I was regularly bouncing around between a half dozen languages when I was doing pro web dev. It was web devs who popularized numerous different languages to begin with simply because delivering apps through a browser allowed us a wide variety of options.
No web dev I have ever met could use Prolog well. I think your statement about web devs being polyglots is based upon the fact that web devs chase every industry fad. I think that has a lot to do with the nature and economics of web dev work (I'm not blaming the web devs for this). I mean the best way to succeed as a webdev is to write your own version of a framework that does the same thing as the last 10 frameworks but with better buzzword marketing.
Generally speaking, all the languages they know are pretty similar to each other. Bolting on lambdas isn't the same as doing pure FP. Also, anytime a problem comes up where you would actually need a weird language based upon different math, those problems will be assigned to some other kind of developer (probably one with a really strong CS background).
That you haven’t met any webdevs using prolog probably is because 1) prolog is a very rare language among devs in general not just webdevs (unless you count people that did prolog in a course 20 years ago and remember nothing) 2) prolog just isn’t that focused on webdev (like saying ”not many embedded devs know react so I guess it is because react is too hard for them”)
Maybe they were, but these days everything must be in JS syntax. Even if it is longer than pure CSS, they want the CSS inside JS syntax. They are only ultimate polyglot as long as all the languages are actually JS.
(Of course this is an overgeneralization, since obviously, there are web developers, who do still remember how to do things in HTML, CSS and, of course JS.)
