since 1.) the module is stored in a .h file 2.) the .h file is included at the top of .F90 files 3.) the routines for which modules are declared are mostly C routines that do not live in a module
as a result should one actually "use" the module in eg con2prim then one would get a link time error looking for the non-existent fortran module routine
I probably also creates all kinds of race conditions to have the same module defined in more than one source file, it also carefully circumvents the Cactus module tracking mechanism.
It is highly confusing and misleading to have the module present when in fact it cannot be used.