Way back when, the difficulties and time involved with game development, and game magazine lead times, seemed to organically evolve a situation where game publishers had their PR and even development arms intertwined to a degree with the print magazines. In order to get your write up, article, or review into the appropriate issue, the journalist / reviewer had to be given advance copies of software. And much of the time those weren't retail products. They were pre-gold "reviewable" code, that was promised to be a fair look at the final product.
In a way, publishers still have to get reviews out before games release. But now it has to do with hype marketing, meeting quarterly estimates, meaning most sales will be within the launch window. So getting reviews out there early is important to them.