[lispm]

Because it takes some effort to write a good Lisp book. There are several very good books: SICP, PAIP, AMOP, On Lisp, PCL, LoL, ...

Also typical Lisp hacker won't buy a slightly edited and printed version of the HyperSpec or a printed version of the SBCL manual.

Add to that that Lisp made a deep dive after the AI winter and that they were sure to not sell enough copies. At that time it was also a good idea not to be connected to Lisp.

Plus, I guess they did not like Lisp. 'Clojure' has the 'advantage' not to use 'Lisp' in its name.

[CJefferson]

I suspect the answer is more simple than you make out. They will not publish what they are sure will not sell.

[lispm]

LISP