Re: Why didn't the Borg...
I think the main theory about this is that the time travel was a hastily-constructed Plan B.
There was a technobabbled explanation in one of the novels that in order to time travel successfully you need to do so near the planet or what-not that you intend to impact. Hey, I didn't say it made sense.
The first DoTI novel speculates that the time travel in First Contact
wasn't the Borg's idea either, which I alluded to upthread.
It was the best of Trek, it was the worst of Trek...
"If I lean over, I leave myself open to wedgies, wet willies, or even the dreaded Rear Admiral!"