The number of entries in the list match with the frequencies obtained by parsing the database.
Iohannes and Maria are both good examples here since they represent 15% & 27% of their category in the database used to establish the list (out of 6000 characters, which makes it the largest one for the mod) : it's logically the names that get the more entries, so these ones will appear more often ingame.
Note that this is a equalized in the final list, because Iohannes would simply be 100 times more common than the least common first name. Also some dynastic & starting characters names were added to match descr_strat file (because previous generations dont always have common names).