Why was the "roach" not implemented into the Penumbra Series?

[PerfectBlue]

To be honest I did not find any of the enemies in Penumbra to be scary. The atmosphere is what makes the game so foreboding. For instance the wolf enemies have no feet.This may be a small critique, but small details like this can remove some of the immersion.

The reason I would include the roach would be, not because its scary, but to introduce more creature variety into the game.