I get the impression that the communities are different. Not that Julia's is "more energetic" (there's actually quite a bit of activity around CL too), but that it's simply a different crowd. The Julia people seem to me to be coming more from the application side of things - computational scientists who want to do a certain job - while the CL people are more interested in CL as a language, without a specific application field in mind. So although neither of the communities are especially large, the Julia bunch have been more focused on good libraries for scientific computation, which is why their ecosystem is better in that respect. (Also, the "Lisp curse": scientists are more likely to choose Julia as a new language, because it looks more like the languages they already know.)

Source: I do computational biology with Julia, hobby projects in Common Lisp.