It's because of non availability of LHB Coaches with NCR.
Total 4 rakes are required so that both Dehradun - Prayagraj Express and Dehradun - Kathgodam Express can run on a daily basis.
Till now NCR had only one LHB rake out of 4. So they were running 04113/14 with single rake.
Now they have arranged a new rake so with that...
more... rake they will run DDN-KGM exp on a tri-weekly basis.
Right now, One LHB rake belongs to 04113/14 and another rake belongs to 04126/25
When 2 more LHB rake becomes available then both these services will run on a daily basis