I don't have to read any articles or studies to see that there is a direct correlation between pornography and sex crimes, murders, marital difficulties, etc.
Men seem to be more vulnerable to it addiction-wise, although some women seem to enjoy indulging male fantasies which may be acted out in real life and also making money in so doing.
Two major reasons:
1) The number of licenses the FCC grants are manageble from an enforcement perspective. There are (I'm guessing) probably less than 10,000 broadcast licenes. Let's be generous and say I'm really, really, really bad at math and say I'm off by a factor of 50, and there are really 500,000 licensed broadcasters, or 10,000 in every state (there aren't). That pales beside the massive, massive number of web pages which easily goes into the billions.
2)As if that weren't enough, the interenet is global, not American. I'm a click away froma German, Swedish, or Kenyan server than isn't bound by U.S. law.