At that time, rectifiers often consisted of a AC motor driving a DC generator. Which probably could have been moved to customers, but was avoided for maintenanc

At that time, rectifiers often consisted of a AC motor driving a DC generator. Which probably could have been moved to customers, but was avoided for maintenance and reliability reasons (more easy to service one big generator/motor pair than a few hunderes scattered aound the city, making noise in residential homes, ...) Nowadays it would be trivial, a complete motor control for variable-speed 3-phase motors, that could technically of course also drive DC, costs a few hundred dollars/euros. But probably not possible for certification reasons, as soon as you mess around with an old system you have to upgrade it to correspond to contemporary safety standards.