I don't quite see the point in having a global function instead of a global variable

One thing it does buy you is the ability to drop a breakpoint on it in the debugger, and then play with caller to see where you were called from. That is not quite as simple to do with a variable.

In a farfetched scenario, you could also diddle the package's symbol table to wrap or replace the function itself. That's much harder to do with a variable.