Symbolic reasoning AI is mainstream, it was just never related to ML. The debate was between symbolic reasoning and machine learning in achieving AI. Somehow AI and ML eventually got equated in the last decade (in that ML became the dominant AI approach).

Symbolic reasoning lives well enough in things like business rules, we just don’t associate it so much with AI anymore, nor is it done with LISP.

I thought that "Machine Learning" was also a topic for Symbolic AI.

They are generally posited as in opposition, though there is some research in trying to combine them.

Topics like "rule learning" existed already decades ago. Genetic Algorithms. Decision Tree learning. ...