Every data pack except the vanilla one (just named "vanilla") are referred to as "file/My Datapack Name". Since "file/" doesn't add any meaningful information, and is formatted as if it were a folder which it is not, this appears to be a bug.
MC-121977
Data packs other than vanilla start with "file/"
Resolved
Works As Intended
5
This is to avoid ambiguity with where exactly the pack came from. If you had a data pack called "vanilla", it will not conflict with vanilla. Same with mods and other possible sources of data packs in the future.