It's because the distinction isn't meaningful for day to day use. People use and compare languages and their standard libraries as a whole.
I do think people recognize the fact that these two are different things (e.g. when comparing C to a language with a richer standard library it's one of the points that are often specifically and separately mentioned.), but it's just not very useful to separate them explicitely in a comparison of languages from a user's point of view (as opposed to a language designer's point of view).
You can't even wrap them into functions or you'd have to write type assertions everywhere.
Now,you could define a custom Array type with methods, but goodbye type safety. It's funny how sometimes Go works better as a "dynamically typed" language than as a statically typed one.
Ruby on the other hand provides loads of methods for every single "core" type.
This is my biggest gripe with golang; I want to be able to write functional extensions for the blessed generic types (slice, map etc.), but can't. Until we can do things like this, or implement our own generic types, golang will be a niche language.
I don't think so. What you're saying is you want to apply a niche concept (fp, I know it's getting traction, but still pretty niche in the business world) to an OO language and have a hard time doing that. Golang is niche right now too, but the lack of functional ability is probably not going to to hugely affect anything.
I'd disagree that FP is niche; the concepts are used throughout business, and more and more back ends are being written in an FP language. Front ends using JS are being written more and more in an FP style as well.
