I do think familiarity plays a big role. I find the Haskell syntax much more pleasant than Java, even though I'm perfectly familiar with both.

The equivalent signature in Java (if we could abstract over type functions) would be:

    interface Functor<F<_>> {
      <A, B> Function<F<A>, F<B>> map(Function<A, B> f);
    }

You'll find very similar in Scala's `cats`, up to some currying and reordering. [0]

[0] https://typelevel.org/cats/typeclasses/functor.html