My collection of knowledge about Julia and Pluto.
The reason that e.g. Pkg.jl doesn't export any of its functions is simply that it would cause a lot of collisions. using is considered the default for interactive use, or scripting within a project where packages are not updated, while import is the default when writing longer-term code (programming, more than using existing code).
https://docs.julialang.org/en/v1/manual/modules/#Export-lists