I don't find that to be the case at all. I worked with Java for around a decade and I never contributed to a single open source project. Every time I'd see a bug or a feature I'd like to add, I'd open the source and it would be a nightmarish maze of classes and interfaces with business logic being sprinkled across them.

Meanwhile, I've successfully contributed to plenty of Clojure libraries I use, and many people contribute to my projects. Clojure code is far more direct and concise making it much easier to understand the intent. And majority of the code is written using pure functions that can be reasoned about in isolation. On top of that you have an editor integrated REPL, so you can just run any code you're not sure about as you're reading it.