Why does the C-2 left inboard stab not have a rudder?
The C-2 was developed from the E-2 Hawkeye (the one with the big radome).

The radome disrupts the airflow behind, hence the need for the inboard fins (source), they help stabilize the airflow and act as fences for the outboard fins.

Those inboard fins were not needed for the streamlined radome of the earlier E-1 (shown below).



Alternatively they could have extended the fuselage length, but they didn't go that way. The three rudders provide sufficient control in single engine operation, yet are overpowering when both engines are working, which caused early control problems and stability augmentation had to be implemented (source: University of Tennessee, MS thesis, 2002).

The E-2 and C-2 feature rudder authority limiter as part of that augmentation (C-2A flight manual).

And apparently the rudder authority is sufficient enough that the E-2 can turn (to remain in orbit) while keeping the radome fairly level (source).

As to why the right one is the one with the rudder, I don't know. The engines are not handed (video). But as far as I know, a normal force on a laterally placed fin does not change the moment arm around the yaw axis, but I'm happy to be corrected.



Development information on the E-2/C-2 is scarce, so I hope that's sufficient for the time being, I tried to find as good sources as possible.