In my guild we have 70% of members that are serious and "hardcore", 20% that are good players but not driven to the be best, and 10% that think raiding is fun but their not willing to do anything extra to win. As a result we do well in 25 man content because the hardcore majority can cover for the casual minority.

In 10 man there is no room to cover for anyone. When you are going after 10 man hard modes even a single weak player will doom you.

So if 25 and 10 loot was equal my guild would have clicks develop from the hardcore players and the rest would be frozen out. Not the most enjoyable situation.

So why even have 25 man content? My guess is because it feel more epic. Having a bunch of people fighting a dragon makes the dragon seem that much more powerful. The less people the less epic the feel. But as stated in the artical, people are rational and will take the path of least resistance so they will do as little as they can for maximum reward then wonder why it's not as fulfilling as it used to be.