I don't remember the exact situation, but I think this relates to this:

Clojure core was sent a set of patches that were supposed to improve performance of immutable data structures but were provided without much consideration of the bigger picture or over optimized for a specific use case.

There's a Reddit thread which provides a bit more detail so excuse me if I got some of it wrong: https://www.reddit.com/r/Clojure/comments/a01hu2/the_current...

*Edit* - actually this a better summary: https://old.reddit.com/r/Clojure/comments/a0pjq9/rich_hickey...

Dissatisfaction n. 3 is the essence of the problem: "Because Clojure is a language and other people's jobs and lives depend on it, the project no longer feels like someone's personal project which invites a more democratic contribution process". This is a common, and modern, feeling that the more users a certain thing has, the more the creators/maintainers have a duty to treat it as a "commons or public infrastructure" and give the users a vote on how the thing is to be managed and developed. This is, of course, utter horsesh*t.