The main issue is that there are other JVM languages nowadays that don't suck--that wasn't the case back in 2009. So, if you wanted the Java ecosystem but didn't want Java, your choices were quite limited. You had Scala (just ... no) and Groovy (oh, hell, no) and ... Clojure.
Since then, Java, itself, has gotten a lot better, and there have become a plethora of JVM languages since. In addition, a lot of languages now have "package managers" like lein. They have also adopted "default const-ness". So, a lot of the issue is that things that were unique to Clojure are no longer that unique in this generation of new languages. Finally, the JVM ecosystem doesn't have the same enterprise pull that it did 10 years ago ... enterprise installations back then only had the JVM, while now you can generally count on a version of Python also being installed.
Computer language adoption is slow in spite of what everybody thinks. Pick a language that you can use as a tool for the future, and don't worry too much as long as it isn't actively un-popular. You'll have to learn a new computer language about once every 15 years anyway.