First of all, this is not only DC, this is DC series motor, which is given to initially high torque.There are two main reasons for using DC series motor for traction purpose. They are: It has high starting torque which is important in traction system. It requires less power for high torque production because torque production is directly proportional to the square of the armature current.
In addition to this, all trains are using DC motor because of main advantages of DC motor. The traction motor used in locomotive in the train engine is a 3 phase induction DC Motor along with I GBT based on control system, as it provides many benefits. Nowadays, double cage induction motors are using in railways
