Let's read the documentation.

> "preprocess"

The value should be a code reference. This code reference is used to preprocess the current directory. The name of the currently processed directory is in $File::Find::dir. Your preprocessing function is called after "readdir()", but before the loop that calls the "wanted()" function. It is called with a list of strings (actually file/directory names) and is expected to return a list of strings. The code can be used to sort the file/directory names alphabetically, numerically, or to filter out directory entries based on their name alone. When follow or follow_fast are in effect, "preprocess" is a no-op.

Your preprocess subroutine, hi, returns an empty list, so there are no files too iterate over.

Why wasn't the preprocess subroutine called before wanted? Because the directory argument to find() is not preprocessed, wanted is run on it directly. Only the directories' contents that are subject to readdir are preprocessed.