Early trailers frequently show sequences that never appear in the released game. The gap is a consequence of when marketing happens relative to when systems are built.
Announcements come long before the game works
Publishers announce projects early to secure attention, recruit staff and reassure investors, often while the game is still a set of prototypes.
At that stage there is no continuous playable build to film, because the pieces exist separately and have not been joined into a coherent experience.
What can be shown is a constructed sequence, assembled specifically for the trailer, which is a demonstration of intent rather than of progress.
A vertical slice is built to be filmed
Studios produce a small, highly polished section representing the intended final quality, with art, audio and scripting finished far ahead of everything around it.
That slice is genuinely running, which is why the footage can honestly be called in-engine, yet it is not representative of the wider game.
Scaling that quality across many hours is the actual production problem, and it is routinely where the finished product loses ground against the trailer.
Performance is a late-stage discipline
Trailers are captured on high-end hardware with frame rate constraints relaxed, because optimisation work happens near the end of development.
Lighting, crowd density and effect layers get trimmed during that pass, and those are precisely the elements that made the early footage striking.
The result reads to players as a downgrade, though it is more accurately the moment the target hardware asserted itself.
Design changes invalidate finished footage
Mechanics shown early are sometimes cut because playtesting found them tedious, or because they never integrated with the systems built afterwards.
Removing a feature is usually the right call, but it strands the trailer that advertised it and leaves an impression of things being taken away.
Studios rarely explain the reasoning, since discussing cut content invites more argument than the explanation resolves.
Labels are now the honest signal
Footage is increasingly captioned as pre-alpha, target render or representative of a work in progress, and those distinctions carry real information.
Captured on retail hardware indicates something closer to what a buyer will experience, while an unlabelled cinematic promises nothing about play at all.
Reading those labels is more reliable than judging the polish of the images, which says more about the marketing budget than the state of the build.