Part of it is you are misunderstanding sematically what 'Search Files' is. It isn't a search over resource names, but a search of the contents of files. Since directories are not things which have contents in the sense files do, it naturally doesn't search them.

What you really want (IMHO) the 'everything matching' in addition to the 'everything not matching' filter functionality. That being absent is a good point, and one I can get behind.