The question is its own answer.
Are they each better for some reason?
Why innovate on perfection? Or, why not improve the existing lisps rather than create new ones?
I understand what you meant, but I don't know the answer to these questions--before or after reading the article.
(I have given clojure a shot, though, and I enjoyed myself!)
I think the best way to look at this question is to think about who "we" is.
Are the sum total of programmers using lisp coordinating to make a final decision on how many lisps there should be? Certainly not. I don't know all the people using lisp, and I never will. So it doesn't make sense that they're trying to do anything. This community isn't defined in such a way that it's meaningful to talk about directed effort.
There are plenty of reasons to make different lisps without implicitly disparaging the functionality of existing lisps. Perhaps you want to learn about how lisps work by implementing your own. None of the existing languages would help you there. Perhaps you simply have a sense of curiosity about a language feature, and want to implement it somewhere. A less mature lisp might help, if the codebase is smaller and easier to reason about. Perhaps you need to use the JVM for business reasons. Perhaps the JVM is too much for the hardware you're running on, and need a C variant. Perhaps there's one with a particularly useful FFI to another language.
Those forms of excellence do not put Lisp on the JVM, nor give emphasis to multi-threaded, functional programming. Hence, Clojure.