So I know the real world parallel rationale for Khan was the Joker, as in that they had to use the most recognizable villain*. But what is the rationale for the Borg?
Zombie movies sell. That and the Borg are probably Trek's second most well known villain.
Zombie movies are definitely prevalent, but they most certainly do not sell.
And the Borg are not really a villain. They're a race; a set piece. And they're primarily known for their association with the next generation. It seems odd to abandon the next generation crew, but then to use their same trappings.