The Elder Gods' Role in Mortal Kombat
The role of the Elder Gods is usually unclear, but mostly it was to maintain the balance in the Universe to which they also created the Mortal Kombat tournament to balance the harmony and cosmos between realms, requiring ten consecutive wins before another realm can merge another. So far, they have the sacred rule of not interfering with mortal affairs unless it threatened the very existence of the Universe (like Onaga's return) or two, violated the rules of Mortal Kombat. In Mortal Kombat Deadly Alliance, they refused to intervene because it was not yet time to intervene since Quan Chi and Shang Tsung have not yet done anything that would destroy the Universe.
In Mortal Kombat 3/Ultimate/Trilogy, one might question why they didn't intervene if Shao Kahn had begun merging Earthrealm with Outworld. It could be a simple as this- Shao Kahn had yet to fully merge the realms without Mortal Kombat so they didn't intervene. Plus, it wasn't a threat to the overall balance of the cosmos so they left Shao Kahn alone. In the reincarnated timeline, they finally did intervene with Shao Kahn because he had won the attempt to merge. Only then are they allowed to intervene to protect the balance of the cosmos.