As for the OP, my view is that back in 2063 the transwarp network just didn't stretch all the way to Earth.
The Borg having time travel at all is a huge plot hole. If they already had the ability to go back in time and change history, why haven't they already done so and assimilated the whole galaxy retroactively?
However, when we consider that the message sent in Regeneration would have contained information about the future, the Queen could have considered it important to make sure history played out that way, in order to ensure that the message with information about the future got to her. After all, if she started making changes to the timeline the message told her about, it would run the risk of rendering all that information useless.
It's also out of character for them; when they suffer a setback, they just accept it and keep on pushing forward until they overwhelm it by sheer numbers and persistence. (I offered a possible explanation for this inconsistency in my novel Watching the Clock.)
I'd be interested in learning your take, but unfortunately the novels are rare as hen's teeth around here. Could you tell me in a PM?