This.
Thank you.
It looks like someone was actually paying attention to MK9's story mode.
EG: "We are aware of your plight, Raiden."
Raiden: "Then you must intervene on Earthrealms behalf."
EG: "We cannot."
Raiden: "But Shao Kahn.... Liu Kang has bested him twice, yet he still....
EG: "Shao Kahn has not violated the rules of Mortal Kombat."
Raiden: "What? He invades Earthrealm, as we speak."
ED: "Invasion itself is not a transgression. It is the merger of realms that is prescribed"
Raiden: "A DISTINCTION WITHOUT A DIFFERENCE!!!" "INNOCENTS ARE DYING AT THE HANDS OF OUTWORLD!!!"
EG: "It is regretable, but the Mortal Kombat tournaments are not intended to prevent certain outcomes." "They are intended only to maintain balance among the realms."
Raiden: "Please, you must."
EG: "We have spoken."
^^^^
That sounds like Elder Gods who don't care about morality.
Shinnok escaping the Netherrealm is also something that the Elder Gods wouldn't see as unbalance to the realms, therefore it doesn't suit their needs.
Shinnok and Quan Chi taking over and merging all the realms together, to become the supreme overlords / rulers of all that is in existence IS something that would destroy that balance between the realms and bother the Elder Gods, as they are the rulers of all in the MK world, and this union between Quan Chi and Shinnok could potentially jeopardize THEIR position as Elder Gods.
Bi-Han as Sub-Zero, being their Champion, makes TOTAL sense as he stopped their armies before as Sub-Zero and can do it again, stopping Quan Chi and Shinnok from merging the realms, and preventing them from being the NEW Elder Gods (as Shao Kahn wanted to be in MK9).
"Today I become THE Elder God." - Shao Kahn, MK9, final battle intro before fighting Raiden