Wasn't the game in production for 3 years?
"Originally the three-year primary developer rotation cycle between
Infinity Ward,
Treyarch and Sledgehammer Games, in which the model was first introduced in 2012, it was expected to be continued in 2020 with Sledgehammer taking the lead to create a new
Call of Duty entry alongside
Raven Software. Due to conflicts of interest between the two, responsibilities were shifted to Treyarch as they took control over the project, which resulted in developing
Black Ops Cold War in 2020.
[22]"
This is what I got. It seems there was something going between the studios. Considering Activision had to mobilize most of their studios to help the game. The 3 year was the cold war. We have no clue what time it started.
But this bit seems to be interesting
"After
WWII was released, the studio went through a rebuilding process regarding the organisational structure. In an interview made by
VentureBeat about the rebuilding and the path leading Sledgehammer Games to develop
Vanguard, Studio Head Aaron Halon highlighted that "[...] we love our legacy and what we’ve created, but we also wanted to think about the future of the studio and how we could set ourselves up to be even stronger. [...] we're proud of the decisions we’ve made along the way that have led us to where we're at today with
Call of Duty: Vanguard."
[21]"
It could be the reason why activation wanted the game to be developed fast.