And all were knocked out by the attack. The chain reaction inside the network caused all the hubs to collapse, thereby disrupting the Borg's capability to reorganize.
The damage to the Borg was catastrophic, and as I've previously said, there are plenty of races capable of fighting back about right now, and many worlds would enjoy the revenge of preying on the damaged collective. If many of those worlds had nuclear capabilities, it would be devastating to the Borg. The virus did what it was intended to do, and that was to heavily cripple the Borg's ability to regenerate, particularly when you have the Individualist movement (the Resistance), Species 8472, the Kazon, the Federation, the Klingon Empire, etc.
The Delta Quadrant has been thoroughly shown to have some powerful races, but nearly as powerful as the Alpha Quadrant. The Alpha Quadrant would be the focus of the Borg's attention as it has the highest population, (probably, given the stabilization of the Federation, the Klingons, and Romulan Empires). Sure they lost a few million during the Dominion War, but not nearly enough to make a difference.
The Borg are about to be feasted on by the survivors of the races they once attacked. With their inability to transfer forces from one area to the next of the galaxy, the Borg would have a tough time staying together. Though they aren't gone, they have suffered enough damage that will eventually destroy them. Besides, the Queen mentions that the sphere has adapted, but no other ships?
The Collective was pretty much in chaos at that point.