Speculation. The FP community prizes mathematical beauty, for which symmetry is an important factor. It is simply ugly to promote one function argument (which one?) to a privileged role, even if the linguistic side of the brain screams that's the right thing to do.

Re autocomplete, there is no technical reason why auto-complete couldn't trim down the search space based on the arguments of the functions, for example by using reverse polish. But reverse polish is unusual, we really like SVO anyways, and modules as subjects are very useful, if only as an autocomplete anchor, in tooling or in one's brain. OOP/SVO is here to stay for the foreseeable future, and embracing pure functions principle makes it rather pleasant to work with. If only we could decouple 'modules as namespaces' useful idea from all the misguided baggage that comes bundled with OOP, of which the 'active data' antipattern deserves special 'please avoid' mention.