the age of sigmar setting exists to sell bundles of models. The warhammer fantasy setting was a rpg game at first then the wargame came later. That's why it feels deeper- it is. That's why age of sigmar feels shallow- it is. Selling better means they have slammed out new armies over and over with the promise of later development that isn't followed up (unless you have pointed ears or golden armor).
As for the age thing, Warhammer fantasy had the enemy within rpg campaign at this relative time, and aos has soulbound, which appeals only to the ingroup.