Well. if you see the Japanese story they never were united (Sengoku Jidai), you will find several clans like Nobunaga, Takeda, Uesugi, Etc…(Like Shogun Total War).
Italians at the time were city states (Venetians, Genoese, Milan, Papacy, Sicily…).
Teutons were a main monarchy, but suffered by gthe several duchies (Swiss, Dutch, Baviera, Austria, Bohemia and more).
If a “Dravidian” “Bengali” “Mughal” and “Delhite” civs would be made, the people won’t be happy with the other civs and will begin to request the division of the Saracens, Persians, Mongols, Chinese, Turks… would you like to see a great civ like the Turks being splitted into Ottomans and Seljuks?
AOE 2 civs are based on a better known empires or kingdoms, as well major ethnic peoples, but cover the related empires and people.
Indians are based on the Delhi Sultanate/Mughals, but cover the entire subcontinent and you can prove this by checking the Game History (Which mention the Cholas), Their Wonder and the UU are based of the southern Indians, if you feel that they don’t cover the Dravidians, the Devs can just add AI names of Dravidian Rulers.