It's funny because I can't pinpoint exactly what happened, but my jumping off point seems to line up with others. I'd watch alot of NBA up until about 2 years ago. This year, I don't think I've watched more than 5 minutes of basketball. I couldn't tell you who is good, who isn't good, etc. I'll watch some playoffs, but I'll gladly watch about any other sporting event over an NBA game.
I think part of the problem is the old stars are fading away, and the new stars are on teams I don't really care about. Harden, Durant, Kawai, etc. are all after thoughts. Steph is stuck on a bad GSW team. Lebron is about the only one doing anything of significance. Wemby is stuck on a ****** team in San Antonio. SGA is obviously great but boring. Luka can't seem to stay on the floor. Ant is about the only real draw for me right now.
I don't subscribe to the "no defense" theory. I think they are trying to guard. I just think the rules and the talent of the players makes it such that it's damn near impossible to get a defensive stop. And that just makes for a bad product, to me at least.