Delta1 said:
They did transwarp straight to Earth in Voyager's "Endgame." Previous attacks transwarped to the edge of Federation space then warped into the Solar system. Make of that what you will.
It could suggest the Borg cubes were not able to open their own TW conduits like smaller ships such as spheres and the likes.
Voyager shortening their trip by 15 years through using a stolen Borg Warp coil is an exception of course.
It's a smaller ship, and if you want to be able to repeat the jumping process by several times and extend the range, you must have numerous coils working in union.
Although a question remains as to why the cubes were not able to open their own TW conduits.
7 of 9 did suggest at one occasion in Season 7 how the temporal stresses on the Borg cubes hull are excessive when they enter a TW corridor (but that could mean the conduit was open remotely or the cube had to warp to a specific point and jump into the corridor) and that they use a specialized field to keep the temporal sync throughout the vessel.