Why?

Two reasons: guest star Kratos, and retailer-specific fatalities.

I won't completely lift all of the dark tidings from this Gamasutra piece verbatim, but it's bad enough for the game's developers to lie claim that "fans of both games have been asking for" God of War protagonist Kratos to appear in a Mortal Kombat sequel, then use that to justify his baffling inclusion in the PlayStation 3 version of the game.

That could almost be forgiven following the baffling cameos of recent Soulcalibur sequels.

Seeking to compound that fresh pain however, Warner Bros. Interactive has given Gamestop, Best Buy and Amazon exclusive costumes and fatalities for series favorite characters Scorpion, Sub-Zero and Reptile. These extras are to be granted to gamers who pre-order the game only from those retailers. If you're a long-time fan, you likely see this as tantamount to shitting on the franchise, before raping every person, object and concept it theoretically holds dear.

The only possible way to be more disrespectful to series fans would involve driving to their homes individually, stabbing them in the eye, then torching the ambulance that arrives to assist them. Oh, and this would all be done while dressed entirely in human feces, and the entirely fictional liquid incarnation of derision that I had to fabricate just for the purposes of this scenario.

Of course, if that ever did happen, Ed Boon, being the diabolical sonofabitch that he is, would simply laugh, and promise fans a Mortal Kombat/Tattoo Assassins crossover.