Nope. Video games IMO. Cheap awesome entertainment for basically everyone. Everyone can afford consoles and escape reality. Why act out aggression in real life and risk prison when video games let you do all that and more?
Crime is primarily carried out by young men 16-25. They now have a very interesting activity that many of them engage in. There is far less 'hanging around' with dodgy mates on streets with little to do.
The crime decline also didn't occur just in the US but all across the developed world which suggests that Roe vs Wade had less impact than Levitt and other suggest.
By the 1990s consoles had become cheap enough that many more people could afford them.
That and as someone else has said, cheap and available porn. Cheap porn was available by the 1990s in magazines and videos. Online it's now much cheaper and prevalent, but it's been there for quite a while.
And I never said Internet porn. While not free, porn was still cheap and easy to get on cable or satellite, or at video rental stores.
I doubt it was just porn though. I believe that simply getting teenagers / young adults inside for long periods of time (and not just for the purpose of abusing drugs / alcohol) is a big victory (for crime stats, not society in general).
I think there were articles in the year following, at least in scandinavia, about it.
Also note: Prison provides free housing, free meals, free gym, and free healthcare.