Functions are too small to make into a package and dependency. Pure functions don’t have cohesion; they are random snippets of code and nothing more. Who really wants a “cosine” dependency? We’d all really like a “trigonometry” dependency instead which encompasses many “tricky” functions that we don’t want to have to write ourselves.
This is a pretty weak argument. What is "cohesion" and why do we care that modules have it? Joe Armstrong, one of the creators of Erlang, has argued the opposite (http://erlang.org/pipermail/erlang-questions/2011-May/058768): that lots of small, individual-function modules are better than a "misc" module that grows endlessly and may overlap with other people's "misc" modules.
Calling a function instead of writing the code yourself doesn't mean you've forgotten how to program! The real problem here is the cost and risks associated with dependencies in general (both of which are actually lower for single-function modules), and the broken package removal policies of npm.