Your comparison is not apples to apples as you would in practice have a seperation of compilation and linking in your non-modules example. The status quo is more like:

    g++ -c -o hello.o hello.cpp
    g++ -o hello hello.o
    ./hello

When modules were being standardized, there was a discussion on whether there should be any sort of implicit mapping between modules and files. This was rejected, so the build system must supply the information about which module is contained in which file. The result is more flexible, but also more complex and maybe less efficient.

Thanks :)