with due respect to prolog (which is a mindbending language), the proponents of every niche language say the same thing. "it is so powerful that users don't talk about it and that is why you don't hear about it"
I've heard many variants of this with respect to Forth, for example.
The reality is that devs can't stop talking about the languages, tools, and frameworks they use.
The simpler explanation is that next to no one actually uses prolog in productions, because it is, well, a niche language (which doesn't take away from its coolness)
Color me skeptical about "secret weapons".
I know many people that do too and don't talk about it unless you move in the Prolog world.
Here's a stock broker using it https://dtai.cs.kuleuven.be/CHR/files/Elston_SecuritEase.pdf
Java Virtual Machine specifiction is verified using prolog ", implemented the Prolog verifier that formed the basis for the specification in both Java ME and Java SE." https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-0-preface7.html Prolog code -> https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.10
https://kylecordes.com/2010/the-prolog-story
IBM Watson was written in C++ and Prolog
You can often find a Prolog system behind complex scheduling and resource planning systems for example. It's no longer pure Prolog nowadays, you also have constraint logic programming and other solvers hooked in (see my other comment on ECLiPSe CLP, http://eclipseclp.org/) but Prolog is still often the host language. The ECLiPSe web page has for example a reference on Opel, the car maker, optimizing its supply chain with it. Sicstus (https://sicstus.sics.se/) is also present in this space.
In a very different domain, IBM publicly commented on how they use Prolog in their Watson system, the one who won Jeopardy (the name was over-used afterward): https://www.cs.nmsu.edu/ALP/2011/03/natural-language-processing-with-prolog-in-the-ibm-watson-system/