Not sure where this "trilogy" idea started but the second show was basically a remake of the first, albeit finally with the actual HNF actors. And the third was only slightly tweaked. It's not like there's an overarching story arc.
B&T ran close to 30 years before Legal killed it. AoV ran 3 or 4 years before its creator's actions forced Legal to kill it. This show is wildly popular, barring outside pressure, I think Universal backs the truck up to keep it going.