> I wonder why it couldn't use os.listdir to find out whether the directory is empty, and os.stat to find out whether a specific file or directory still exists.

It is possible to do the same thing with just os.listdir.  The use of
the Find*File functions was chosen to eliminate duplicating the wait
function for the two different cases.  Also,  it is just less resource
and time intensive to use the Find*File API directly (no need to build
an entire list when just testing if any entries exist).