Why??
Let me re-phrase....In a perfect world all divers would be practicing the same system.
I don't know about you, but after I was diving awhile I noticed a lot of hack divers out there. I don't care what you practice, DIR, HOG, whatever. We just need to churn out better divers period. I'm not saying I was anything special when I started out. I'm talking about stupid stuff like divers heading out without even knowing how their computers work. Or having enough knowledge to get through a dive without it if they had to. Or not diving 10 pounds overweighted all the time. Common sense stuff.