2nd Engineer DP Vessels

I am currently 2nd Engineer working on a pipe lay vessel in brazil, a class 2 DP vessel, prior to this I spent 3 years on a DP3 DSV in the Gulf of Mexico after making the transition from passenger vessels.
I am interested in gaining a position on a drill ship/rig which is proving to be difficult as they all want experience. What is the difference between the ER of a drillship and a DP ship that makes this experience onboard essential?