IMHO it's just that it's a beam VM language, which is a fatter runtime/ecosystem than is really needed to achieve the goal stated above can bring it's own bag of problems (but also it's own superpowers).

Also to be productive you have to utilize the rest of the erlang ecosystem, so at least some superficial knowledge in elixir & erlang is helpful for for some use-cases.

Syntactically I actually don't think it's that for off, but I dunno what GP was thinking, maybe that it leans more into functional patterns & sugar for those whereas rust/go can also be used in a procedural style. (Though at least personally I am using way more functional patterns in rust than I expected)

Trying to come up with a reply made me realize something. I was initially going to write something like "it's just not ready yet" but paused for a moment and reflected on that. That's actually not a real reason why it would come short of that. And instead of talking about how something "is not quite ready yet" we can instead choose to invest into it and use it anyway, with the goal of contributing and helping make it "ready" and more widely used.

Out of everything mentioned, I think Gleam is the most likely to succeed and what I think I will invest in as well. But that's not just because of the language design but rather because of their approach to community and community building! It's a very very nice extra that the language/syntax also happen to be what I like and have described in my previous comment.