Playtest results inhibit you from disclosing things because they are subject to change. They take gamers’feedback, decide if they want to act on it, and at the end of the day the finished product may look different so it makes no sense for people to loudly state “they have feature X, and they don’t have feature Y” because by release it may be the other way around.
Whereas this type of contract says “idgaf what’s bad about the game, you can only sing its praises online”.