apparently he didnt renew his tna contract and he was in talks with hhh and sent feelers over to wwe last year
The Wrestling Observer reports that WWE is having conversations with The Icon, who has yet to renew his deal with TNA. Sting has said a few times in the past that he has had multiple talks with WWE about working with the company, and has even admitted that he nearly took a deal on one or two occasions.
The dream match that many fans have imagined for more than a decade is The Undertaker vs. Sting, particularly at WrestleMania. With both men in the twilight of their careers, this could be one of the last chances for the match to take place.