..WB owns the rights for MK, I know how marketing works. I know for sure that increasing DLC guests from 2 to 6 within 3 games when no one is asking for them guests with minor expections, in a franchise with tons of characters fans wants to see returning in ONE GAME is for the love of CASH.
The thing is, lots of people
do ask for guests. Terminator and Spawn have been heavily requested since
Mortal Kombat (2011)! You see people asking for guests all the time, on Boon's Twitter, for example. themortalkombat.com used to be flooded with regular guest requests as well.
The guest characters are also the highest selling DLC charatcers in the franchise, so ofcourse they're going to keep making them, and increasing their presence.
Interestingly, they also listen to requests for returning
Mortal Kombat characters, and balance those with guests. Tremor and Tanya, Jason, and Predator were heavily requested during the life of
Mortal Kombat (2011), and they appeared in
Mortal Kombat X. So was Bo Rai'Cho, oddly and sadly, as well as Alien and even Leatherface. Cyrax and Sektor were after
Mortal Kombat X launched. We got them in Kombat Pack 2.
Shang Tsung, Nightwolf, and Sindel were heavily requested during
Mortal Kombat X, we got them in
Mortal Kombat 11. As mentioned, Spawn and Terminator have been hugely requested since
Mortal Kombat (2011), we got them now. Joker's the only DLC character we got that I haven't seen requested before.
I'm not a fan of guest characters myself outside of rare instances, but I've long accepted it's a thing because the casual fan base, which is much, much larger than the competitive fan base, wants and buys them. Having said that, I prefer guest characters to 3D-era characters. Any character added from
Mortal Kombat: Deadly Alliance to
Mortal Kombat: Armageddon should remain buried to modifiers, endings, and comic books (where they seem to quickly die) because they're honestly not good characters. It's actually these characters that have the smallest fan-base, and for good reason. The 3D era was the darkest and lowest point of the franchise for a reason.