The worst thing that ever happened to Common Lisp was its ANSI standardization, which for many years killed almost all language innovation and improvement.
On the other hand, standardization enabled Common Lisp implementations to actually be tested, so programs became much more portable across time and between different implementations.
What stopped further development of the standard was the collapse of the market for Common Lisp.
I should note that many of the things that need changes to the language definition in other languages are just libraries in Common Lisp.
Nobody stopped anyone to come up with variants, just from calling those ANSI Common Lisp compliant. There are after all many, most of which are long dead already.
