Also, that's not a listing of the total number of libraries; it's ranked based on the number of useful ones (where "useful" is a completely subjective term that relates to how often I've looked to see if a library exists that does what I want).
Racket actually has more overall libraries than you'd expect considering its popularity, but I've found that many of them are old, no longer updated, scheme libraries (from the days before Racket rebranded from Dr. Scheme). That certainly doesn't make them useless, but I'm reticent to mix scheme-style code into my project.
I'm least familiar with Clojure (I've only been deploying it for the past two weeks or so), so I'm sure my opinion will change, but right now it feels like a slightly less good Racket with a philosophy I find agreeable and more practical libraries (plus Java interop).