When AI couldn't live up to the hype, funding dried up. A lot of that funding was driving the companies and research projects that were doing major Lisp development. After the AI Winter, Lisp was strongly associated with the unmet promises of AI and thus gained a reputation as a poor choice for serious projects.
Around 2000 a new generation rediscovered Lisp. SBCL was released in dec 1999. CMUCL rethought with a simplified implementation and build process. From then on various implementations were improved. Clozure CL was released on multiple platforms. The commercial Lisps were moving to the then important operating systems and architectures.
The hype moved to Clojure, Racket, Julia and other Lisp-like languages. The core Lisp may not have the same depth of commercial activity as in the 80s, but generally the implementations are in the best shape since two decades. There are still lots of open issues, but from the Lisp programmer standpoint, it's an incredible time.
https://en.wikipedia.org/wiki/AI_winter
When AI couldn't live up to the hype, funding dried up. A lot of that funding was driving the companies and research projects that were doing major Lisp development. After the AI Winter, Lisp was strongly associated with the unmet promises of AI and thus gained a reputation as a poor choice for serious projects.
It's never really recovered.