It's in Deception's story mode.

At the beginning of time, the universe was just an empty void and the only thing alive was a creature called "The One Being" and the Elder Gods. The Elder Gods fought a war against the One Being and killed him using a weapon called the Kamidogu.

The One Being was shattered into pieces and those pieces became the realms. The Kamidogu was also broken into six pieces, which were hidden on the six most important realms, Earth, Outworld, Edenia, the Netherealm, Seido, and Chaosrealm. The only way to put them back together is with Shinnok's Amulet, because it was also made by an Elder God and contains most of Shinnok's power.
The people of the realms are formed out of the One Being's subconscious thoughts, and sometimes these thoughts can influence major villains, like Shao Kahn and Onaga, and make them think merging all the realms or all the Kamidogu back into one is a good idea. It's not though, because it'll recreate the One Being.

What all this essentially means is everything in Mortal Kombat is a dream and if he ever wakes up, it'll destroy all of creation.

Basically, this means that Mortal Kombat entirely futile on the long term, since everyone aside the primordial Elder Gods (so Raiden exluded) is a part of the subconcious effort to reunite the realms.

This means, that for example, if Liu Kang and co. would win continuously in MK tournaments for whatever reasons beyond defense it would also surmount to reuniting the One Being.

They are boned.


And the Elder Gods are apathetic assholes, morally ambigous. Evil in a certain way if you wish.

Not quite sure what you mean there. The whole Mortal Kombat tournament was designed to prevent the take-over and merger of realms, so if the defending realm won the contest 10 times in a row, the realms would remain separate. That seems to go against the whole reuniting concept of the One Being when guys like Havik, Ermac, and basically every Earthrealm hero has constantly fought against that idea of unity.