You're not wrong on the whole Gaia and Alaya watching earth. Yet last I recalled, both did nothing when Gilgamesh was unleashing a bunch of mud from Shinj-Grail, nor did it do anything when Sakura started her rampage. Compared to a few Grimm, the Shadow was worse.
That, and the Grimm have yet to be recognized as a threat to humanity as a whole. Doubt both entities care if they attack a city and rampage.
That, and the Grimm have yet to be recognized as a threat to humanity as a whole. Doubt both entities care if they attack a city and rampage.