Maybe in order to take GOW to the next level you need new blood? I don't know.
Personally, I have zero interest in GOW.
I could more likely see a situation where they brought Cory on and he wanted to make a new ip but Stig had a team working on a new ip as well. The studio head basically saw two new ip's as risky and decided to cut one and have the second team double down on GOW.
This is all speculation and based solely on the possibility that GOW is being made, or at least planned.