I looked at Fable and the resulting code just looked way more complicated than anything Javascript could write. I'm interested in F# still on the backend, but I don't think people "haven't discovered" Fable, it's just not a great alternative.
Three years of building with it (plus constant re-evaluation of that decision) has supports our conclusion that it is far more concise and easier to manage (esp for less technical folks who need to sign off on the business logic/domain) than anything we'd have done in JS.
With that said, we're building a product that requires much more interactivity than most, and we're performing a lot of typical "back-end" logic in the client - that might color our evaluation.
To be sure, it hasn't been without tradeoffs, but we haven't found those tradeoffs to be at the language level.
Like, I have seen a little of both (I've used a lot of TypeScript, but who actually looks at the output JS lol), and while I agree the JS output from Fable seemed surprisingly verbose, I'm not sure I see how it practically matters unless one is worried about bundle size or something.
For whatever reason, F# to me looks surprisingly verbose in Fable, which is odd because it's pretty terse on the backend.