That's basically the crux of it, syntax matters a lot less in language adoption. Most mainstream languages benefit from a "killer" app, feature, software-class

That's basically the crux of it, syntax matters a lot less in language adoption. Most mainstream languages benefit from a "killer" app, feature, software-class or platform, which is what sees Swift become hugely popular because of iOS, Java/Kotlin getting a boost from Android, Browsers popularizing JS and many games & OS Software still written in C++ for its zero overhead abstractions. Ecosystem, native libraries, community, knowledge, tooling, familiarity, domain suitability, hireability and overall general dev productivity & UX matters a lot more in language adoption. I'm not seeing any big draw card from a Killer App that clearly highlights its superiority over more popular alternative languages. There's many niche areas where FP shines like implementing compilers, statistics & math models, but I don't see much appeal in mainstream usage where it adds enough value over dominant languages to overcome its deficiencies in other areas. A clear example is AI which is an area that FP would excel at but is still dominated by Python & its dominant ecosystem. The value proposition of pure FP languages also gets diminished as mainstream languages adopts FP language features.