When I say a AAA trailer can cost "about four months of development iteration time", I don't mean it LITERALLY takes four months to edit a video. I mean that's roughly how much disruption gets spread across the team.
The first month is goddamn death by a thousand cuts. Producers and Directors need to figure out what the trailer is trying to say. Teams are pulled into meetings. Features get reprioritized. Artists, designers, engineers and QA all have to estimate what they can realistically contribute. Nobody stops working entirely, but everybody for sure loses some momentum.
Then you can have a period of intense focus where parts of the team temporarily pivot away from buildin the core game. Artists gotta create bespoke assets. Engineers are hacking together functionality that only needs to work in a controlled environment. Designers have script moments that sell the fantasy that takes so much iteration to get right. QA has to maybe validate a slice of the game that may not represent the wider experience. Because you can't showcase something that looks well but doesn't play well, (and then you're stuck with bullshit that looked good in a trailer). For a month or two, a significant amount of creative energy gets redirected toward the trailer.
BUT GUYS IT GETS EVEN MORE ANNOYING WHEN THE TRAILER SHIPS.
The month after is often spent stitching all that shit back together again. Teams gotta resync, all the damn plans get rewritten. All those features built for the trailer get integrated, or re-scoped (or ABANDONED???). Feedback from execs, publisher, press, or the public might even create new priorities. Not ot mention people have to remember where they left off before the interruption.
A whole bunch of people gotta take a couple days vacation after the trailer if they had to crunch for it. The trailer migtt only be three mintes long, but every AAA game development i worked on ran on momentum.
It's not that everyone suddenly stops working for four months. It's that hundreds of people each lose little chunks of time, and eventually those chunks add up to months of development momentum disappearing into the fucking void.
I'm trying to teach everyone how Game Dev works but it's too many words sometimes.