As Rich has said, Clojure is small and intends to remain so. Clojure has everything you need right now. It doesn't need gobs of new features to be sufficient. Most Clojurists are hard pressed to come up with things they really need in the language itself, so the rate of change in the core language has slowed. (And the rate of change in the tooling and libraries around Clojure gets more attention now.)
> they are disinterested in promoting the language and ecosystem beyond selling their database software
... is incorrect. We have every desire to promote Clojure as a language (regardless of Datomic). Could more be done, sure that's always the case. Please help promote Clojure by doing great stuff and telling people about it!
I also believe that tools.deps is a step in the wrong direction, fragmenting an already small community and forcing all tools to support yet another dependency/build system.
Leiningen is super powerful, and it was never made clear what kind of conflicting requirements / philosophy led to the birth of tools.deps etc. In absence of an official answer, the presumed answer is Not Invented Here Syndrome.
Wouldn't you consider this and official answer?: https://github.com/clojure/tools.deps.alpha#rationale
I mean, Java is pretty much the biggest ecosystem there is and it's trivial to use Java libs from Clojure, so I'm not sure this is a fair comparison.
The Go ecosystem seems pretty weak outside of the standard library. I'm not an expert, but I was trying to fix something the other week and was shocked by how few packages there were to solve my problem. The main one (which is a dep of things like k8s) is currently unmaintained.