Without a top down mandate, what else can you expect?

In OSS ecosystems it's usually plenty of choices, or nothing.

See NPM registry or choosing DE in Linux.

Within the rust ecosystem, rust has tokio as a clear winner for async runtime without a top-down mandate.

There are a couple of alternatives, but none of them come close in popularity

Akka seemed to win in Scala

But then the main contributor, Lightbend company, decided to change the license from Apache 2, to BSL.. Now Apache Pekko is the fork that should continue the implementation :)

There's a class of software project where it isn't very hard to bash together a simple thing that solves a good chunk of the problem, not covered by the language itself, but has endless elaborations you can put on them.

These rarely stabilize in the sense you mean, of there being exactly one sensible choice in some domain. (Note difference between "rarely" and "never".)

See also: Web framework, Javascript GUI framework, serialization libraries (easy to write the parser(s), endless combinations of ways to handle the resulting JSON for you), and these are just some big frequent examples that leap to mind. There's a lot of these sorts of things.