Because pre dark below hitting level 30 was a big step and in the process of getting everything for it you had to play a lot and when you play a lot you get more Grimoire score. You being level 31 with that kind of Grimoire score proves that you did not work as hard as the veteran players (like myself) to hit level 30 then 31. Ask almost anyone who has been playing since launch and grinded countless hours to hit level 30 and 31 about seeing a level 31 who has obviously not grinded or played as long as us about hitting that level with that Grimoire score and you will get then ranting (I would). I have seen level 31s who have not even done the VoG before! I believe that it should be mandatory to do the VoG to hit 30 to then buy level 31 gear from the vanguard.