Because, WWE acquired WCW and Sting did not want to work for WWE. He wanted to continue his professional Wrestling career and when TNA offered him a good contract, he joined them.
Watch TNA Now, NO!
I think its STING!
In January of 2014, Sting was in a match against TNA wrestler Magnus in a no disqualification, no count out match for the TNA World Heavyweight Championship. Due to Sting losing he match his contract was terminated. In February of 2014, TNA confirmed Sting's departure from the company.
nO HE HAS A WIFE
no he is in tna.
Sting was with the NWA (National Wrestling Alliance) and WCW (World Championship Wrestling) before he joined TNA
he went to tna