Because HG DOESN'T own the entire macross series itself (again, this is the core of the whole debate in the first place, but I digress), but what Tatsunoko owns, which is "The right to sell the show overseas, and the general right to exploit merchandise." - according to the now infamous memo, which most of us here tend to agree that this is what was said.
Now the most recent ruling gave Tatsunoko ownership of the animation for SDF Macross, and the line art still recides with Big West/Studio Nue.
So, why would HG "own" the rest of Macross, when it has been quite clear that the only thing they bought (via TP) was the rights to the animation.
That being said, if HG want's to bring the other series over, they'd have to get in line with everyone else, and bid/buy them from BW.
On the topic of Mac7 Trash.
All HG said is that they were "cooperating" with it's release. Now, this is VERY ambigous, as it could very well mean that they are licensing it to Tpop. On the other hand, it could also mean that they're not doing anything to stop it; wether they have grounds to do so or not.