Because Clojure ignores Lisp.
Put that gun down, and let me explain.
Lisp is a process. Progress is measured in decades.
Lisp gets lexical scope right, for example, simply because we have a head start of decades over the
I'm quite certain that the unwashed masses will discover macros around 2020 and hygiene around 2040.
It's simply a matter of time.
Lisp moves slooooooooooooooowly.
And because of this slowness, individual contributions simply don't matter. They're just a blip on the radar. You can measure a programmer's inexperience by the amount of saliva generated by new, unproven language features.
Yeah, great, Clojure does some newfangled stuff with persistent data structures. Well, if it works, Lisp will adopt it in a couple of decades. In the meantime, we'll just keep on using the same tools we've been using for decades, well.
Yeah, great, Clojure has some semi-solution for hygienic macros. Again, we'll see how that plays out in a couple of decades.
If you have some great new idea for PLs, you can be quite certain that Lispers heading an Ivy League university's CS dept have already tried it out, decades ago. And if it isn't in today's Lisps, it's because it didn't work.
So what do I mean when I say that Clojure ignores Lisp? Well, it ignores the fact that individual inventions in Lisp are mostly meaningless, because Lisp is a community process.
For the larger Lisp family to adopt a feature, it has to be tried out and implemented in a dozen different dialects and implementations, over the stretch of decades. Until that happens, it didn't happen.
And there have been and are so many smart people in this community, that if you think you've got the great new idea to push Lisp farther, you're wrong.
(I'm surely not one of these dweebs that say CL is the be-all/end-all of Lisps, and we should all be using it. Hell no. Everyone should be writing new Lisps! It's one of the greatest learning experiences there is.)
Now, go ahead and have fun using Clojure if it floats your boat, but stop whining about how it's a more modern or better Lisp. That doesn't make the slightest bit of sense.
Why do you glorify doing something new and stupid, when doing good things well is what people really should be admiring. — Linus Torvalds[Update: this is a rant. I'm not writing articles. The good people at HN have pointed out the many flaws of this rant.]