Language preference, ergonomics and isomorphic code have not been good enough use-cases to get people off of Js

But they are good enough reasons for people to want to use it over JS when coming experience with rust backends.

There was a big hype around compiling to Js a decade ago, but that hype past us and nowadays

What do you mean? This hype never passed - this is exactly what typescript is, a compile to JS language. And TS has taken off as a language and adopted by a large amount of people working in the web frontend world and with JS in general.

Writing frontend code in Rust really isn’t going to make a material improvement over writing the same thing in TypeScript, unless you need raw performance which is less than a percent of all webapps.

Developer satisfaction is a good enough reason to pick a language for something (assuming it outweighs other tradeoffs). And if you have picked something like rust for your backend then there is a good reason to also use it for your frontend - assuming your devs are more experience in rust than JS and you have no existing JS code you need to interact with. Performance is not the only, or even main reason you would want to pick rust over JS. There are a lot of other reasons it can be beneficial.

Having a single language, however crappy, did create some much needed stability in the frontend space

Stability in the frontend space? What are you talking about? There is a new framework or library or even compile to js language every week. The web platform is just a fast moving target now you are constantly needing to learn new things to keep up with it. And adding more optional things like other languages does not make this any worst or better - but does mean those that are not already familiar with JS, but are with other languages can use the language they are familiar with instead of the whole fast moving JS ecosystem.

It is also quite handy that frontend engineers can focus on their job, not on learning language X with toolchain Y and libraries Z.

And if you have people familiar with JS already then there is not as much point in getting them to learn the rust eco system. Just like it is nice that if you already know the rust eco system you don’t need to learn a JS just to do frontend development. And JS developers are already constantly learning new frameworks and libraries as the churn in the JS eco system is quite high.

but I’d rather have a single okay language that gets the job done with a good ecosystem then a dozen competing ecosystems some of which may be better in some respects

I disagree. Having more languages available on the web is better IMO. It gives more people more options to get into it and you are not stuck on some language that was created in 10 days 28 years ago and only recent years had any improvements done to it at all. Yea, most people will still use it and there is little to no point in converting existing projects to it. But that does not mean we should not be exploring different languages in the web space at all. Or being forced to only use compile to JS languages. It is all optional, you are not forced to use it. But it lets those that want to use it do so.