The "top" modifier does not improve results. At best, you might find a text file listing "top 10 GTA mods."
The addition of the word in the keyword adds a crucial layer of intent. It suggests the searcher isn't just looking for any old directory listing, but for one that is high-quality or complete—perhaps containing all the necessary game archives (like .rpf files), installation setups, or even cracked .iso files.
When combined, the query instructs Google: "Find open server directories that list downloadable files specifically containing text related to the top elements of GTA 5." What Users Look For in Open Directories
If you insist on understanding the search landscape (for educational or archival research), here are legitimate variations of the "index of" dork that data hoarders use.
However, several factors have rendered this method nearly obsolete today: