There's still a LOT of quality talent on the roster:
Styles Angle Sting Wolfe/McGuinness Angelina MCMG Beer Money Dinero/Burke Doug Williams Ayoko Hamada Joe Hardy (debatable, but a big name) Morgan (debatable, I guess, but he's really improved) Rhino (debatable) Team 3D (debatable)
For nostalgia value, they also have some of the biggest names of the 80s and 90s on the roster, including Hogan, Sting, Flair, and the Outsiders. Even with their recent talent departures, they could still be putting on a strong wrestling product.
They just AREN'T.
Do you guys remember the actual origins of Conan O'Brien's Masturbating Bear? Even though it became popular just because of how weirdly random a giant masturbating bear is, the character originally started off as a bear who would go into a flying money booth to grab cash for a needy game show contestant:
The gag was that even though the contestant really needed the money, and even though the money was RIGHT THERE in front of the bear to grab, the bear would always, frustratingly, use its hands to masturbate rather than grab even a single hundred-dollar bill for the entire time. All it had to do was just stop masturbating for 2 seconds and grab some money and everything would be fine. It had everything it needed to succeed, but left to its own devices, it always went off and screwed up right before everyone's eyes.
The company already has some outstanding wrestling talent and some of the biggest stars of yesteryear for the nostalgia value. It's not like they're hurting for yet another new wrestler to sign that will bail them out of their jam. Signing "Big" Dave Batista won't rescue them any more than signing Van Dam, Flair, Hogan, or Angle did.
It's like, if you described TNA to a friend of yours who's a casual fan that hasn't been watching wrestling in recent years, you could point out that Impact has Hogan, Flair, the NWO, and Sting, as well as Kurt Angle who really goes all out in his matches, plus three high-profile ex-WWE stars in Hardy, Van Dam, and Anderson, plus the cream of the crop of the indies--AJ Styles, Samoa Joe, Nigel McGuinness, and up until recently, Chris Daniels, though other indie darlings like Brian Kendrick, Amazing Red, and Homicide also hang their hat there. Your friend would be all like, "wow, that sounds awesome." And you'd have to explain, "no, sorry, actually the product kinda sucks."