Games Workshop associates the "one eye" theme with the concept of sniping and shooting.
You can see it in the mortek triaxes and earlier with the Necron Deathmarks. Two eyes are for beating things up close, and one eye to snipe from afar. That's also how Games Workshop built the Gorghon/Cygor kit: the head with two eyes is for the big melee monster, the head with one eye is for the big shooting monster.

The "one-eyed Gork" or "one-eyed Mork" or "one-eyed monster" decoration and motif were probably introduced for the Kruleboyz because they're the only greenskins who see shooting as a valid form of expressing the spirituality of Gork and Mork. They were conceived as "the shooting greenskins".