You constantly have to use Java libraries. Which means you have to understand the Java ecosystem. Which increases complexity a lot, since that ecosystem is very

You constantly have to use Java libraries. Which means you have to understand the Java ecosystem. Which increases complexity a lot, since that ecosystem is very mature but also often deeply layered, complex and full of historical baggage This problem is bigger in Clojure which has a smaller ecosystem than Scala and is why I don't pick it for writing "real world" applications in it.