Warner Bros. Interactive Entertainment has tried for months to get the Xbox 360 and PS3 version of Mortal Kombat X to meet the same quality standard set by the next gen version of the game. However, despite their best efforts, they could not meet that standard. 

Community Admin Yorick on WB Games’ community blog says:

The older system version of Mortal Kombat X was originally meant to be released sometime in the middle of 2015. However, the older system version was eventually delayed into the later half of 2015 before eventually being canceled.

For those who had order Mortal Combat X on either PS3 or Xbox 360 should visit the retailer they preordered with. People who preordered on either of these systems are entitled to a refund. 

Mortal Kombat X is still available for only Xbox One and PlayStation 4.