The thing that killed TNA more than anything else was that they made a lot of the same mistakes as WCW - Chiefly they got Hogan involved in creative and his little circle. In those days the product even looked the same as WCW. The 6 sided ring went, the usual suspects got hired, the emphasis was put on names over the "TNA Originals", like Joe, Daniels, Styles etc
The only company where Hogan is a benefit is in WWE, because they're big enough to keep him in his box. But to go back to the point of the discussion - a p*ssed off wrestler with something to prove can be very damaging to a former promotion - provided they're allowed to have free reign. Ryder for example is a very charismatic guy, and lots of people would follow him if he moved somewhere where he was allowed to shine. WWE want to avoid giving this embryonic potential rival any weapons they can.