I don’t have numbers to back it up, but I’m making inferences. Clojure is only 10 years old. That’s far too brief a time for it to have acquired a large user base. That’s far too brief a time for it to have matured as a language.
Smalltalk has a long history. Consequently, it has amassed a substantial worldwide user community. There are several major Smalltalk vendors (Cincom, Instantiations, GemTalk); they have many enterprise customers around the globe.
ESUG (European Smalltalk User Group) is a vast organization. INRIA, the French national institute that does research in computer science and applied mathematics, has been actively developing Pharo for years.
Common Lisp, the only other “major” Lisp remaining, is somewhat marginalized by comparison. And no wonder: Common Lisp is a complex behemoth, sort of like the C++ of the Lisp universe. Nobody really wants to use it.