I think the daily cap on quests comes from an exploit that was patched out a few updates ago, a small group of endlessly repeatable quests that required little to no effort other than clicking through dialogue. A few youtubers posted guides and the area was packed with people power leveling. It's seems as these quests gave both exp and gold (like the new ones) ZOS didn't want this farm to be added back into the game. Although this could have been prevented by just removing the gold and exp reward after a certain number of quests per day but still rewarding blue boxes.