Unfortunately this is sometimes true. Manuals written too early describe half-implemented software that is later changed or removed in the final rush to production. Conversely, if the manual is written too late, writers madly write, cut and paste together whatever they can find in a desperate attempt to cover most issues, somehow. Publishers assign writers whose longest prior effort was a ten page college paper, then profess surprise at their inability to handle a 100-page manual job. Good manuals instruct the player, enhance the gaming experience, and explain away problems.
Every publisher bemoans the extra cost imposed by manuals.
Instead, the gamer just got a CD and some advertising leaflets inside a big box. The manual was in files on the CD, which could be read or printed out from your screen. This was a sales disaster. Gamers weighed and rattled the box, and judged the product wanting. Reviewers excoriated Sierra.