I think they put this mechanic in there (making 50s do low lvl fates for item gains) to make the low level places more populated. In FFXI that was a problem and coming form the same company I believe they are trying to avoid that. Starting grounds before the beach had only a few people and I would guess in the later years the beach was sparse (I played in 03). Also, they include some fate mobs (going back to 14 lol) that require a party and in thus the 50s help in that matter.