Because we got prophunt. Just an idea
Because zombies has more of a cult following. Infinite Warfare Zombies last map The Beast from Beyond had cryptids in it.
Extinction was a blast to play and I was one of those hoping that they would’ve carried it on.
Saying the reason that Extinction didn’t return because Zombies had more of a cult following I don’t really buy that as the reason. zombies had been attached to numerous games already so the sample size was much larger and if that were the case why create Extinction in the first place?
But then again I was also a fan of the challenge game modes that some of the earlier cods had, juggernaught , the snowmobile race.
I had fun playing Extinction too, invested a lot of time into it. More than Infinity Ward bringing Extinction back, I think we both would have preferred they took a bigger step and went with Ghosts 2.
Obviously I don't know the real reason, but I can't help think SHG and IW took the Zombies route because they saw the success of Treyarch Zombies. Activision probably thought it was a no-brainer and keep it as an offering every year... regardless of what the devs had in mind.