AmmoLoad, Camdex and a couple of others use electric motors for their mechanized presses, and they load a lot faster than a shotgun press.
My MEC 6000GE uses an electric motor and it works fine for the slow operation of the shotgun shell loading, as would hydraulics.
I think it's due to the electric motor being less complicated and easier to control for fast operations. When you throw in hydraulics, there is a whole other aspect to the system with the pressure system, hoses, couplers, etc. It's just easier to control them with the electric motors and some micro switches, without the hassle of the hydraulics, especially when you're loading at the rate of the metallic machines. I used to average about 1,500 rounds an hour with the AmmoLoad, and that was stopping to fill the primer column and powder hopper. Bullets were fed from tubes, and I could change tubes without stopping the machine. And that wasn't pushing it at all. The machine was capable of loading faster than that, but I didn't have any need for loading faster at the time.
At least that's my thought, having used the AmmoLoad in the past.
Hope this helps.
Fred