The only way they could do more than one story about the Borg was by changing the concept to personalize them more.
As was kind of observed upthread, the Borg have some similarities to zombies, and multiple zombie stories can be told without personalizing them. In fact if memory serves, the similarity of the Borg to
zombies was the problem, Braga and Moore had intended to write the Borg as faceless adversaries in First Contact
before the similarity to flesh-eating undead was pointed out.