By policy, LISP has never really catered to mere mortals.
The thing I notice about Common Lisp is that people who use it tend to be geniuses by my standards. Read Planet Lisp for example. Or the Common Lisp mailing lists. There you find posts like (to paraphrase), "I just wrote a 12-line macro that allows recursive lazy evaluation of infinite series!" (EDIT: Apparently this post was a joke. Phew.)
As I mentioned before, according to someone who interviewed me for my last job, he often had difficulty even finding a programmer who knew what the word "recursion" means. How many programmers in the world know what lazy evaluation is? How many programmers in the world have a need to use infinite series? How many people in the world would be able to understand that macro, let alone write it, let alone use it for anything useful, ever? I know what recursion is, I know how it's useful, I know what lazy evaluation is, but I do not understand that macro nor can I think of any even remotely possible situation where I'd in my wildest dreams consider using it for anything.
It seems that this is the kind of programmer the Lisp universe caters to: The most power-tastic of power user imaginable. The level of assumed knowledge is enormous. Assumed knowledge about Common Lisp itself, and assumed knowledge about what I'd call advanced topics in computer science and software design. Read the documentation for Elephant as a good example of a tool designed for someone far beyond my capabilities. I tried and mightily, fantastically failed to get Elephant to work for my needs. Oh how I failed. It was a failure of truly epic proportions.
With Common Lisp it's not so much a learning curve as it is a sheer cliff face in the middle of the road. Documentation is sparse, and where it does exist, it's terse and extremely technical and bare-bones. Tools and libraries have gaps and quirks and it's just plain expected that you'll be able to easily fill the gaps and fix the quirks yourself. Libraries tend not to be the kinds of things you can download and use and get away with not knowing the details of how they work. Instead of an easy-to-use straightforward library, you often end up holding the remote control to a maniacal super-powerful flame-throwing sword-weilding death machine which can just as easily burn your house to the ground as it can solve your problem for you.
Meanwhile there are people like me who can barely get Common Lisp's object system to work right. I can just barely operate the text editor that I need to use to write Lisp code in the first place. Here I am still struggling to write a simple photo blog in Common Lisp. It's been well over a month since I started. I have something that almost works but I'm embarrassed to look at the code and certain parts of it I just can't get to work right. I feel like it could be so much better if I knew how to use this language properly. I could go ask for help, and sound like a moron. I'd feel like someone posting "What's a command line?" to a Perl mailing list. There's a certain amount of R-ingTFM that you have to accept as necessary. But never have I felt this frustrated or unable to figure out what the heck I'm doing.
It's like my goal is to build a box. Ruby or Perl or PHP give me rudimentary tools like "hammers" and "nails". Common Lisp gives me a drawer full of electrical components that an engineer could use to build a box-building robot capable of constructing boxes of arbitrary sizes from arbitrary materials. But all I want to do is build a freaking box. Sometimes I wonder what the heck I'm doing here.