You have to take into account that it's not just about displaying a file list like the old DIR command in MSDOS.
For my previous test, a DIR whose result was put in a text file took only about twenty seconds to finalize.
each file is subject to a number of mandatory tests for display in the web page, additional data associated with it even if some are empty in the end.
All data associated with a file on the disk is stored in a temporary memory record, and this space is freed after each refresh of the web page. converting this data to web representation takes a few milliseconds, depending on the machines, but this repeated action countless times may look like an eternity.
The VFS keeps this data indefinitely, whereas for the real files and files, it amounts to constructing a new building each time to create spaces there, to store carefully what will be used, then all methodically to clear to have a new location for the following requests.
we can see this as an album of photos for which we must at each consultation by the web systematically recreate the thumbnails