For reference, I am talking about the Battle of Sector 001 in the movie "First Contact."
I can understand that the Borg were busy dealing with species 8472, and that's a reasonable explanation for only sending 1 cube, but why wasn't a tactical cube sent for the second assault of Earth if a regular one had failed before? It's not like tactical cubes would have helped them fight against species 8472 anyway.
The 1st cube was nearly unstoppable. And the queen spending resources to create an assimilation virus shows us that the Borg were still interested in assimilating Earth. The name 'tactical cube' implies this is what that type of cube is designed do to. So instead of possibly wasting another cube the second time, why not send a stronger one?
If you sent a cube that almost worked, wouldn't you send a stronger one the next time?