A big reason is the intake.
The intake at DTU is 1600, which is much higher than the average intake of a given government engineering college such as IIT or NIT. Furthermore, due to the high intake the competition for placements and academic excellence has become much more fierce. While competition is not bad, it can become slightly exhausting considering the students have already been through the biggest competition of their lives for two years to get admission to DTU in the first place.
The fees at DTU is also slightly more. This is why most students prefer top NITs such as Surathkal and Warangal over DTU.