their is a big reason behind it...the concept was introduced to increase seating capacity and to provide journey in the busiest routes...but the reason by which it is failed is its type...seats should have been good...
Passengers as before taking WL's and managed to travel, after intro of DD somewhat adjusted but now they again are taking WL's in older trains...thus DD fails...
Seats should be same as Shatabi's have to increase its priority...