Traditional large ROVs are designed as square cages pushed through the water by large, powerful thrusters.They are not particularly hydrodynamic in any one direction, and require several thrusters (some lateral) to turn and maneuver.
VideoRays work differently the result of years of design and testing. They are designed to move forward well, and to spin on their axis so they can easily point in the direction they need to go. This spin capability is a result of the sophisticated float block shape, the wide stance of the horizontal thrusters. It allows VideoRay to maneuver and seeĀ whatever is needed, and this design is critical to working in currents too strong for most vehicles in this class.
For the most part, the addition of a lateral thruster would provide additional drag with minimal improvement in capability. An analogy is four wheel steering in cars manufacturers discovered that the additional benefit in parking and high speed lane changes was not nearly worth the additional weight, complexity, and cost, and the feature was only available for a few years.