There may be another consideration
Cassini is big and heavy. I don't know, but it wouldn't surprise me if it was already near the interplanetary payload limit for the Titan IV booster, the heaviest lifter in the US inventory. If that's the case, then the extra weight for the gimbal system might've had to be compensated for by reducing something else, most likely fuel. Admittedly, the mass limit might not have been a limiting factor. They might've been able to launch a slightly heavier Cassini and made adjustments to the trajectory to compensate. I'll have to do some checking and see if that's the case.