I'd simply say that 3D was a sort of gimmick to add to the repertoire of the PS3. I'm certain Sony figured that it would be the next best thing, as it was a fairly big deal on the movie scene two years ago, but now it is settling back into its relaxed state where nobody really cares. They can do it if they like it, but most won't really bother. Simple enough, but true.
If I had to theorize as to why Sony made such a big deal about it, then stopped really trying to push it so much? The television division and the losses they were having probably contributed, considering they were trying hard to get their sales back up, especially of 3D TVs. Now that they're trying to restructure and it's become more obvious that that sort of television is not going to take off like HD in recent years, they are much better served trying to push other aspects of their business that will offer more lucrative returns.
It's also a personal opinion that Sony was trying to test the waters for the next generation. I've had the discussion with many people, over and over, that while the PS4 and 720 will be impressive graphically, what else can they really do? There really isn't much mainstream that's better than 1080p, if anything, so what will differentiate the next generation beyond better hardware? All of the big three are trying to aim for the next big thing to catch on. Always have and always will. 3D might have been one of Sony's horses they were trying to bet on to see where it went. Mixed results, obviously, but seems to me they're likely putting their money elsewhere now because they've seen the response.







