I made a post about this type of stuff a few pages back in this thread.
TNA does not actually have a huge roster of regulars. They have some (and not even all of them wrestle in every show)...but 2/3 of their listed roster was full of talent that was part time...and they were paying them a flat fee, whether they worked much or not. Tara hasn't been working a ton in months. The knockouts and the lower card talent (think X-Division) basically rotated around the year where you'd have 3-4 on the road at any given time, but they were paying for 7-8-9 of them. Even now, you basically have Gail Kim, Taryn Terrell, Velvet Sky, and Mickie James working...you got nothing to do for ODB, so, you make her a ref. You still have Tessmacher signed, but you don't use her. And think, you had Madison Rayne you were still paying, Tara and Taeler Hendrix recently, too. That's four talents you weren't really using, but paying anyway. And heck, you're probably still paying Christie Hemmie a good amount to announce. They still keep SoCal Val around to do whatever it is she does. You're probably paying Brooke Hogan way too much.
They pay for chicks that don't do a whole lot. They are probably paid beans, but I guess those beans add up especially to a company that doesn't make a whole lot of money.