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It didn't die per se I would say, it mainly got subsumed into more general programming and problem solving patterns (search, heuristics, A*, that sort of thing). What probably "died" is the dream that those would be sufficient to achieve general intelligence.

"Symbolic" AI is very much used wherever you have theorem provers e.g. z3, no?

Yes, and closely related are various forms of constraint solvers, things that LLMS are still fantastically poor at.

SMT Solvers are used extensively in certain parts of the industry, especially when working in security-mindful fields.

Nothing existing only before 1985, that is, before the invention of the open source, was alive in the first place. The code for the classic programs is nowhere to be found. And if found, it is written in some interlisp dead language.