IMHO Clojure's omission of reader macros is sensible: it prevents proliferation of custom syntax, which makes it harder for a human to read code and reason about reader behaviour. The Clojure reader also already has its own literal syntax for vectors and maps [] and {} (which eliminates the most common use cases for reader macros).

If you believe that standards are helpful, then surely one standard reader behaviour is a good thing?

Regular macros are a different issue: they allow creation of custom control structures that aren't possible with normal functions. That's a powerful and useful feature, as many Lisps have proved over the years.

So Clojure rejects the former (unnecessary syntax sugar, potential for confusion, dubious value of reader proliferation) and accepts the latter (additional semantic power, proven utility). I personally think that's a good trade-off. YMMV of course.

Of course, there's nothing stopping you from implementing a custom reader in Clojure if you really want reader macros. So far, nobody (to my knowledge) seems to have cared enough to do this.

NOTE: I'm not bashing Common Lisp: just pointing out that language design has real trade-offs. For me, Clojure gets the majority of these design decisions right. For others, maybe reader macros are an essential feature and Clojure therefore doesn't work. No problem, use whatever works for you.