In a way, all trains are electric. Big diesel trains drive a generator. that generator powers the electric motors on the axles. It is a very efficient way to deliver power to the wheels without a gearbox. The benefit to having multiple electric motors is dynamic braking. Each electric motor produces power from the trains inertia. When you want to slow down, one motor is switched electrically to another motor except the polarity is reversed. This way both motors are trying to create electrical power, but they are fighting each other. The result is that the train uses its own inertial to slow itself down.

The engineering challenge with all electric trains like the model in the picture is that the overhead cable must deliver all the power to the train which is a bunch. There are two ways to deal with that much power. Giant cables and giant contacts with low voltage or small cables and very high voltage. Either way, the total energy that can be delivered has limits without burning up the sliding contact which is why all electric trains must pull a lighter load.