AMillionHP
[13] Hero
It's because Rock was unpopular and had a story that literally had nowhere to go besides Bangoo.
The REAL issue I have is not Rock being gone, it's nothing ever being done with Bangoo. If anything, Rock should have been killed by Asty in SC1 and then Bangoo could have taken over his role, which would have allowed far more freedom in the creative writing department. Astaroth being around means in both story and gameplay Rock is redundant, considering Astaroth is literally just 'Rock, But Better In Every Way' in both Canon and Gameplay in pretty much EVERY game.
The issue with Rock can be summed up in three things: appearance, voice and most importantly moveset.
If those three things are addressed, nothing else will matter.
Edit: lol now that i look at what i typed, thats everything. What else is there to a character in a fighting game really?