Guest characters and non story characters are equally a bonus, but the fact of the matter is is that each character is a chunk of development time and money. This is mortal kombat, so many of us mortal kombat fans would like to see our Kabals and Noob Saibots and Rains an Smokes here in mortal kombat, the only place theyve ever existed. So when those characters dont show up, and characters from random horror movie franchises start showing up it is a little discouraging. The producers said "we have a budget for another character" and the conversation seems to have possibly moved to guests with some favorites on the table.
And i have to say the horror movie guests thing still feels left field to me. I remember before Freddy was spoiled one user said he knew it was Freddy and we all thought he was the biggest troll. I could see someone from injustice or another fighting game, or a popular action game but the rampant horror movie presence is something that just seems really random to me.