Poor Cthulhu, you spend all that time waiting for the stars to be right, You finally get some gullible cultists to give you a boost, and what do see when you finally hit the mainland?

Zombies.

Now there’s no one left to turn mad. Sure you could still devour the zombies, but that much decaying flesh in your diet is bound to give you incredible gas. Cthulhu’s gas would be powerfully bad.