A lot of Lisp was funded by AI research. That research dried up in the 90s (see "AI Winter"). Regular computers of the time were underpowered for Lisp, which or

A lot of Lisp was funded by AI research. That research dried up in the 90s (see "AI Winter"). Regular computers of the time were underpowered for Lisp, which originated on mainframes and then moved onto purpose-built hardware. So the new generation of programmers learned Pascal, C, and C++ instead and were mostly disconnected from the AI research that had come before. Modern AI focuses on numeric methods, whereas classic AI was heavily symbolic. That makes Lisp less well suited for it, since symbolic computation is where Lisp shines. Classic AI does have some useful bits to it, but insofar as AI development goes it's mostly considered a dead end.