At $4 I don't care if my 25' dive is done on air or nitrox. I only pump nitrox into my tanks at home. It costs me $2 more. And I don't know where I will use them when I fill them.I doubt that ti is a significant revenue stream. It seems more like a way of deterring nitrox so as to keep it simpler. No issues matching tanks to divers or analyzing.
Btw, I couldn't imagine using nitrox for a 25' shore dive.