The reason I have not adopted DIR...
As I understand it, DIR preaches minimalism, if that's the right word. Simplify everything, don't over-complicate things. But, they also say to use a long hose (I can't remember if it's 7' or 9'). I'm sure this reccommendation came from the need for divers who are sharing air to swim through a narrow cave single file. Makes sense. But, to say you need a hose that long on an open water rec dive, seems to be a contradiction. IMO, 4' to 5' is long enough for open water, especially in a kelp forest, where you don't want to get too far from your ooa buddy. Anything longer increases the risk of entanglement.
Also, DIR leaves no room for solo diving, pony bottles, and integrated lp inflator/2nd stages. I admit, I haven't read anything from GUE, and if I'm wrong about DIR's tenets, feel free to set me straight. If I was doing the type of diving the WKPP crowd is, I'm sure I would adopt more of the DIR philosophy. But, I don't think it's the best system for every type of diving, and I doubt if it was originally designed to be.
As always, just my own two pennies. Answering why I haven't adopted DIR.