One thing that does always strike me about such libraries is that they are often relatively easy to use for common scenarios like that, and the mental model is really not so complicated or abstract as to require category theory or something like that. When you use such libraries, I don't think you are really doing deeply category-theoretic thinking. More so just seeing how the types fit together and maybe thinking of some higher-order functions that you want to combine and apply.

If you take Haskell and remove all the types (e.g. Scheme or JavaScript), you can have all the same abstractions, with basically the same syntax and operational behavior. But then of course the operational behavior is just applying/composing functions in the end... And because there are no higher-kinded types to deal with, category-theoretic language is less likely to sneak in.

I say this as someone who has used Haskell for years and studied category theory / PL theory as well. And I like all of those things, just think it's sometimes not really necessary to get the mental model at all and be able to use those tools.

I think that some code duplication is also not always the worst thing. Just because strings can be "combined" through concatenation and numbers can also be "combined" through addition does not necessarily mean you need one general notion/function to capture both, especially because if you take that to an extreme then you end up with some function that "sqoogles the byamyams" (i.e. the abstraction has become so general that the only way people really understand/use it is by looking at its concrete instantiations).