That’s only true in some instances. Do most AAA titles like Call of Duty, GTA, etc use Unity or Unreal?

The IW Engine is basically UE5 at this point (for your CoD example.) The fact that it's a proprietary fork is fairly irrelevant to it still being assembly-line work.

In the last few years the pendulum has been swinging back from inhouse engine to Unreal Engine. There are a couple of holdouts, but my guess is that the majority of AAA games currently released are back on UE - at least it feels that way ;)

And Unity always ruled supreme for AA and mobile games.

Most massive studios have their own which they use across a bunch of titles