I think the journey of a Lisper inevitably ends up with realizing that Common Lisp is not an acceptable Lisp. Then you start searching for an acceptable Lisp. You look at Tcl, at Prolog, Io, Rebol, and Icon; you learn Shen, try Scheme and Racket, appreciate Smalltalk and Self and Slate, wrap your head around Forth and Joy and Factor… and the whole time you write Common Lisp. Because there is no acceptable Lisp.
I fit this description minus a few of the PLs you listed, and added Extempore's xtlang, PicoLisp, and LFE (Lisp Flavored Erlang), but I am hacking in CL again this week!
.. and, finally, you realise that Common Lisp is an acceptable Lisp (because when you learn it well enough you start to understand how to tune it to make it acceptable for you personally ;)
Because lisp is an immensely flexible language/concept. Everyone has their own idea of what it should be/can be.
Common Lisp was exactly what it says "Common". Just some sort of common ground between all the various lisp dialects that existed, because everyone went their own way in extending the language. People end up coming back to it time and time again, because all the others don't quite provide that common ground for people to work on. Whilst there may be things missing, there's always something more missing in other lisps.
