Which is weird because it would imply that communications don't change over the course of history, and boy would that be a bold assumption to make.
Or the method of communication of whales is already so perfect that no improvement is possible/necessary, which is unlikely.
I suspect the writers were strongly influenced by Noam Chomsky's ideal that the fundamentals of language are hardwired...scientific consensus is still unclear on this, but it does at least seem plausible.
In the context of the film, it's quite possible that these aliens had intermittent contact with humpback whales for millions of years, constructed probes to rapidly learn the basics of the whale languages they'd encounter when they arrived, and had no reason to anticipate the rise of humanity (anatomically modern humans only having existed for maybe 2-10% as long as humpback whales), the sudden extinction of the sentient species they knew of, and failed to include contingencies for them. The assumptions required for the chain of events presented may have been reasonable ones for a species that had experienced nothing analogous to the rapidity of human societal evolution, or the on going extinction event humanity is responsible for.
Or maybe they were just writing a story and didn't fuss too much over the details...