It has nothing to do with quality (there are lots of good quality out there), but all to do with free content.
Conversions have and will find a new bottom each time the industry decide to give more free away... Anyone who have been in business for more than 8 years now this, because it has happen again and again.
Sure people might grow tired of specific content, models or even fear billing, but the vast majority of surfers use porn when mastrubating, and if they couldn´t get it for free, then they would be paying for it - maybe not monthly but atleast a few months per year to get some fresh content
