It looks like the dat files are missing or have been moved from the online database location. If you open up a dat file in the DatabaseFiles directory and it says 404 not found, then the online database file has been moved. I’ll see what i can find.
The dat files were located
https://github.com/libretro/libretro-database/tree/master/dat/[SYSTEMNAME].dat
but looks like many are gone now.