A lack of interest in the story, combined with the rise of The Hulk + Eric Show. Never liked HH and EB; for me, they have been drawing XPac heat since almost 1990. So naturally, when you bring them in and make them the focal point of the show, I'm going to be a lot less interested. I stopped watching TNA because they stopped giving me a reason why I should watch.
I'll get to the specific moment I stopped watching TNA in a moment; but first, ask yourself a question that was asked by Mr_Ratings; why does TNA catch crap for their lousy writing, while the WWE gets a pass?
The answer is in what the story is about. A good story- any story, from "War and Peace" to "Curious George Cooks Some Meth", speaks to our morals, and professional wrestling is no difference. In its most basic form, professional wrestling is a morality play with fake accolades to fight over. The WWE is offering a fairly bland script right now, but they're sticking to basics. A cocky, arrogant heel eventually gets shut up by the strong, smooth-talking guy with good manners. Human traits that are undesirable are mocked and defeated; desirable traits are exalted and glorified. There's a reason Steph's hired a room full of 20-year olds for creative; they work cheaper and this stuff really isn't that hard.
In those veins, what does TNA offer? How does Fortune turning on Immortal affect my own personal moral compass? (If it's good writing, it should, but it doesn't. All good writing has an emotional impact; I'm not prepared to argue that statement, because third-grade teachers should have already made that point for me.) TNA's writing exists in a zone of moral ambiguity; instead of the heels existing to give contrast to the traits of the face, the face exists to give the heels someone to beat. There is no personal investment into the product; just looking at these boards alone, some of their biggest boosters aren't fans because of the excellent storycrafting, but because they want to watch wrestling and really don't like the WWE.
As for the moment I stopped watching? October 14th, 2010. The "THEY" storyline ended exactly as most people thought, with Hulk + Eric going "it was me, Austin, it was me all along." But they did throw one surprise in there- Jeff Hardy's heel turn. And as disappointed as I was in the "They" reveal, I thought I'd turn on Impact to see how TNA was building on it. Would a heel Jeff Hardy become the focal point of the product? That was a development I could have gotten into! But instead, the show started with Hulk + Eric talking for 25 minutes about how great they are. (If I thought either man had a shred of humility in him to begin with, I could have read that as a plot point, but they don't.) Jeff Hardy comes out 25 minutes into the product. Here it is, I thought- the big "it's my time" moment from Jeff Hardy where he gives us the "why I did what I did" speech.
Instead, he stammers for 45 seconds and then passes the mic back to Bischoff.
It was then that I realized that nothing had changed, and that nothing would change so long as Hulk + Eric are affiliated with TNA. Considering that the only place I'd like to watch Hulk + Eric on television would be as the protagonist in a real-life rendition of "The Running Man", and that TNA would continue to center around them, I came to the conclusion that TNA had offered me nothing, and did not appear as if they would offer me anything to be interested in in the near future.