Lisp's market share was declining 30 years ago and only continued to decline. Python's has consistently risen in that same time. Also, Lisp offers little benefit, if any, when all the ANN implementations rely on C++ and CUDA code. You can write fast numerical code in Lisp, but it's not as straightforward and it's certainly not an idiomatic or common way to use Lisp. That could have let it compete with the C++ libraries, but wouldn't help with the GPU programming part. Lisp could have been the glue language like Python, but again, Python's popularity was on the rise and Lisp's on the decline.