Geographical considerations brother.
The landforms here are having very diversified elevation throughout the journey. Maintaining 130kmph in an nearly uniformly elevated track is quit easier as compared with variable geography. Still the Rajdhanis here have nearly 80kmph avg speed between Nagpur-BPQ-Kazipet which is quite acceptable. They don't hit continuously 130kmph like the Mumbai Rajdhanis or Howrah rajdhanis, but these south Rajdhanis do hit 130kmph for limited amount of duration.