TNA gets a consistent 1 rating on cable. If what they pay for a 1 rating is better than what they would pay for a .3 rating with a Charles in Charge/Joanie Loves Chachi block, then they keep TNA. If not, you'd have 2 of the greatest themes in television history on Spike.
And it's free. And there's a much more wide variety of it than nipple slips on WWE. And it's available for viewing 24 hours a day, 7 days a week. I've never understood people's fascination with WWE nipple slips.