Time to Complete the Game
Speed is the name of the game when it comes to releasing relevant content for an outlet. Whether it is releasing a review or breaking a news story, there is a substantial amount of payoff for being first. However, often when speed is involved, inaccuracy and a lack of thoroughness can be found. This is also true when it comes to reviewing games.
Embargoes are often set in such a way to provide adequate time for a reviewer to play at least a significant portion of the game before putting the pen to paper and giving their thoughts. This helps safeguard against reviewers who get the game and, in the spirit of expediency, put together a half-baked review just to say they were the first to publish.
In this way, the embargo acts as an incredibly pro-consumer construct by not incentivizing reviewers who are attempting to cut corners to get their review out ahead of everyone else. Even though this doesn’t completely stop someone from putting a couple hours into a game as long as say, The Witcher 3, and speaking on it definitively, it does allow readers to have plenty of options to discern who didn’t give the game its due diligence.
Conversely, the embargo could give a reviewer adequate time to uncover a bug that may not affect the game until 20 or 30 hours in. This is something that may not have been discovered had a reviewer only been able to give a few hours with the game before writing.