I am guessing here, but the power center that the Paralax converter/charger is in appears to be a standard RV type, complete with both the 120 volt circuit breakers as well as the 12 volt
side, including the converter and fuses. Apparently Paralax is the only one who makes such a combination, and it is convenient for the RV manufactures to use it rather than supping an individual 120 volt circuit breaker panel, a converter/charger, and a 12 volt
fuse panel. The RV manufacturer deals with, and wires, one device, rather than three.
Paralax does not make a unit, as far as I can find, with a 3 stage converter/charger section, so if AS wants to use the single box system with all 120 and 12 volt
parts in one unit, they cannot buy it with the 3 stage converter/charger, and no one else makes one which has all three parts either.
Now Progressive Dynamics makes a converter/charger with 12 volt fuse panel which fits directly into the Paralax box, but they do not make a rival total 3 part box that a manufacturer can purchase. So, for AS to use the single box 120 volt circuit breakers, converter charger and 12 volt fuse system, they are forced to use Paralax equipment. I can remove the guts of the converter/charger and fuses but they cannot, and have anything which is cost effective for them.
I am speculating of course, but bet I am close to the real reason that AS continues to use the Paralax single stage converter/charger.