Gaming is very different than what it was ten or even five years ago, and one of the main differences people notice is that AAA games take an incredibly long time to make. If a large game started development now, we would likely expect it to be on the next generation of consoles.
Mark Darrah, BioWare veteran and current consultant on Dragon Age: The Veilguard spoke about what takes AAA games so long to make on his YouTube channel. In the 25-minute video, Darrah explains why we're seeing games get announced years before work even begins.
According to Darrah, it's important that the game is in public consciousness, even if the developer won't be working on it for a while. "It might be because the publisher's slate is a little weak, and they want the public to remember it still has important games in its back pocket. It might be because the studio wants the game announced because they're worried the publisher might kill it otherwise," he said.
<social>https://www.youtube.com/watch?v=8NK0vKRf0_c</social>
As well, studios apparently give the impression that this faraway game is in development parallel to a studio's priority, which Darrah states pretty much never happens. Other factors like the size of a game, the team involved, and how detailed the features are can also mean a game takes nearly a decade in development.