From Creatures Wikia
Grendels was a game design proposed at in mid-1998 at Cyberlife, at about the time Creatures 2 was being released. The objective was to change grendels from their rather one-dimensional portrayal in the existing Creatures series to two (or perhaps even three!) dimensions. This might have been one reason that they were relatively friendly in Creatures 2.
In the end, it was deemed not yet possible to make the game as intended. If Creatures 3 had been more successful, it might have been possible to move on to Grendels at a later date.