The electrics, like the later diesel-electrics, produce more tractive effort at slow speeds than steam engines. As I recall the original box cabs were semi-permanentely coupled in two unit sets. (Over the years they would be rearranged to different multiple unit combinations.) Steam engines would have to be double or triple headed, each using an engineer and fireman to move the same tonnage one engine crew could do. The electrics also had regenerative braking that could feed power back into the catenary, in theory a train going down hill could help power a train going up hill. Having a contract with the power company to take back electricity produced by the railroad, after the first official run it was announced that the power company owed the railroad money for the run. The train produced more electricty going down grade than it used going up.
Doing more with less and at less cost. Essentially the same battle would happen again when diesel-electrics challenged and then vanquished steam.
Jeff