Nicer to read is pretty subjective, but I'll tell you why I've switched 2 projects from Python and Ruby: speed. Our systems just had too much to crunch through, and the global interpreter lock pretty much killed us. We switched over to Clojure in 2009 and never looked back. In the early days, we had to wrap a lot of Java, but it's been several years since that was necessary. Currently, Clojure + Kafka + Apache Storm is the scaleability trifecta.
One final comment, which is often tragically overlooked, in my opinion: ease of deployment. Package management and deployment often sucks in other languages (especially in Ruby). By contrast, Leiningen is a SWEET dependency management tool, and the built-on-Java approach leaves you with a jar that you scp and you're done.
I do most of my work in python, and don't plan on switching any time soon, but after playing with Clojure I sure do miss leiningen over the mess that is pip / virtualenv / conda / zomgihatepackagementinpython.
anecdotally, a lot of go's adoption was likewise driven by python and ruby programmers looking for speed while still retaining some "high-level language" features.
One final comment, which is often tragically overlooked, in my opinion: ease of deployment. Package management and deployment often sucks in other languages (especially in Ruby). By contrast, Leiningen is a SWEET dependency management tool, and the built-on-Java approach leaves you with a jar that you scp and you're done.