Not of This World Not of This World is a colorless counterspell, and potentially a free one, in the right circumstances
You want to fight Grothama with big creatures like Ghalta, Primal Hunger and Mossbridge Troll to kill it and draw bursts of cards
Because the creature with exploit isn't on the battlefield, its other triggered ability won't trigger
And, of course, the more lore the better
Even though there are matchups where we want a ton of counters (like Izzet Epiphany and against various control decks), with nine counters in our sideboard, we couldn't find the room to bring them all in, even in the matchups where they are great
Granted, the overall historical momentum has been for it to keep moving earlier (understandable since the Summer slot came into existence, and then later into prominence), but clearly WotC is at liberty move the Spring set around at will