TNA released Tara as a cost-cutting move. Regarding Doc's release, his contract negotiations went on too long and his deal expired. Doc had been figured into creative plans with an eventual babyface turn.
Doc's departure is being blamed on Bruce Prichard, head of Creative and Talent Relations.
Regarding Rob Van Dam's release earlier this year, one source claimed to PWInsider that RVD stopped getting his phone calls returned by TNA officials.
Tara was also apparently far and away the highest paid Knockout in TNA and the decision was made to shift that money elsewhere.
More TNA releases are expected and sources insist to PWInsider that they will continue to change various things in the company.