10 Dumb Mistakes Star Trek Wants You To Forget
2. The Borg's Priorities Change
The Borg had a somewhat stilted entry into Star Trek canon. They were originally conceived as the parasitic race who were teased in Coming Of Age and then introduced in Conspiracy. The idea of colonies being scooped right out of the ground was then introduced in The Neutral Zone. However, their design and drive was radically overhauled for their final/first appearance in Q Who?
They became the cybernetic beings that the audience would come to know so well. As many will be aware, the main drive of the Borg would be to add the 'biological and technological' distinctiveness of other races to their own race. Check that word - biological.
In Q Who, Q states clearly that the Borg have no interest in the Enterprise's crew. He maintains that they are only interested in the ship's technology. This would become a continuity error by their very next appearance, with that next appearance being The Best of Both Worlds. From that episode on, assimilation would become their main drive.
It is highly unlikely that Q, the omnipotent being, would be unaware of the Borg's drive to assimilate all civilizations, so this is simply a mistake in the history of the Collective.