Why do most smart cars use DC reduction motors (such as TT motors) instead of DC motors?

Generally, for the same type of motor, the output speed and torque of the reduction motor with a gearbox are in an inverse growth state, that is, the greater the output speed, the smaller the torque, and the smaller the output speed, the greater the torque. Because the required torque and speed of the car may not be fixed, the reduction motor can be adjusted in this process. If you use a DC motor, if the one you buy does not meet the usage, you may need to buy a new one, which is not so flexible and takes more time. Generally speaking, the reduction motor with a gearbox will be cheaper if it meets the requirements, and the range of available sizes is larger.