I understand what you are trying to say but you may be oversimplifying. PADI does have something to do with the price of every course, by setting costs for the training material and admin fees (i.e. cards) that are required of the course. If they set the cost of the training material at $0 then they would have nothing to do with the cost of a course. I understand that those fees may be a small portion of the overall course fee, but it is still a part and is therefore instructors have to take those costs into account when setting their prices for courses.
I also understand your analogy on inflation and the cost of the courses. You appear to discount that costs for things tend to go down over time as efficiencies and scales of production increase, that is a normal market trend. Another perspective might be that the OW course you took in the 50s taught you x,y,z (as has been talked many times in other threads on old school training vs new school training); wheras modern courses only teach you x and you have to take AOW, plus a specialty to get y & z. So a true comparison would have to include the skills you learned in your class in the 50s compared to the total costs of courses to get those same skills today, and then adjusted for inflation.