Author here. I started it as a side project to have a local-first, org-mode outliner web app to use on my phone. I chose Clojure/Clojurescript because I'm more familiar with both compared to Javascript/Typescript. Several things I like a lot about Clojure/Clojurescript:
Data-Oriented Programming, all three (logseq, roam, athens) use Datascript, which is an in-memory database and Datalog query engine.
REPL (as other lisp languages)
Clojure is very stable, I can run all my old projects without any issues.
Also, I don't reverse engineering the Roam code(it'll cost more time for us), Logseq is hugely inspired by Roam Research, Org Mode, TiddlyWiki, Workflow.
- Datascript: https://github.com/tonsky/datascript