The best part of being a JavaScript programmer is that you have the entire world working for you for free.
Of course, this is very much a double edge sword, with all the "leftpad" type dependency nightmares and security issues, as well as the "Hot new JS framework of the month" issues. Still, I think the dependency issues are solvable and dependency tooling is getting better, and the frameworks issue has calmed down a bit such that it's easy to stick to a couple major projects (e.g. React, Express) if so desired, but more experimental, cool stuff is always out there.
Better to depend on numerous 800 pound long-lived gorilla's than a million short-lived mayflies that keep dying.
PS: I have already poked my head into the Kafka codebase in the past. Not the best written project and also confusing because of the Scala mix, but far more readable than several I have seen. And Java makes it easily navigable. Can even auto-gen diagrams to grok it better.
But it has so much of a broader ecosystem of other tools that if you're willing to take that risk it's an option. Java basically just doesn't have that.
You might say "so what they're doing it for free, you don't have to use their stuff", but often you do because the existence of a sort-of-working solution means that other people are much less likely to write a robust solution for the same problem. So everyone ends up using the crap one.
Rust and Go are way way better in that regard.