Reddit is a tough example, because of the plethora of subreddit topic areas. Almost every sub blessed with "default" status (visible logged-out and a default subscription for every new user) suffers extraordinarily due to their significant reach -- which is in line with your point. Example: /r/pics.

There is still good content on Reddit if you find the good subs and learn to ignore and not perpetuate the overt sexism and racism that decorate that site like Christmas. (I think those are more to blame for killing Reddit. Internally, I'm calling it 4chanitis.)