Completing all possible achievements in the game gives only 1e6% damage buff, that's only 1e4 damage. Absolutely insignificant boost, tiny reward for completing ~1000 quests, some of them are hard and needs days to finish. Veteran players deal around e1000 damage and e4 achievements bonus is not motivating to finish them.
Same as game is not motivating to finish all ~2000 patron variants, you need to finish only 2 for each patron to get almost everything game offers.
Game need some extra mechanics, quests, rewards... something.