They had been separated from the Collective for a long time, and likely were attempting to return, which is what Borg tend to do when separated.
We've seen this before (Or is that in the future?) when Hugh was found. Despite his desire to assimilate, he did not try to mount a suicidal attack on the Enterprise D. When some of his individuality returned to him, and he realized he could no longer feel his connection with The Collective, his desire to return to it became very strong, and when given the opportunity he immediately left to re-join them. Though he and his fellow borg in his Cube were eventually separated from the Collective, this was a decision of the Collective, and did not occur until after he was re-united.
Likewise Seven of Nine, immediately after being 'rescued' from the collective, and even after having her implants surgically removed, had an intensely strong desire to be returned, stronger even than her imperative to assimilate the crew. It took the collective efforts of the rest of the crew to help her fully regain her individuality.
Even Picard during his tenure as Locutus was strongly affected by the assimilation, later admitting to his Brother that it had been all to comforting and tempting to remain with the Borg, even for the brief period of time when he was assimilated.
It seems like being part of The Collective instills an incredibly strong desire in the individual to remain a part of that Collective, and when separated they do everything in their power to return to it.