Are there weight/performance reasons why an electric truck would need a multi-speed transmission? Most electric cars only have a single-speed
Food for thought though, trucks are much much heavier loaded than cars. 100-150+ tonne vs like 1.5-4 tonnes for a car. Cars are trivial by comparison.
Perhaps the motor they have available doesn't have enough torque for it without gearing down.
This is true of cars too - the single-speed transmission in a Tesla is a 9:1 reduction gear, for example.