Source: Wrestling Observer Newsletter
In the latest edition of the Wrestling Observer Newsletter, Dave Meltzer reports that Robert Huffman (King Booker) quit WWE when he was told that he was to be suspended for 60 days, as a punishment to the Signature Pharmacy bust. He was believed to have failed a Wellness Program test before, hence the 60 days suspension instead of 30.
While WWE is still trying to negotiate Huffman's staying with them, they're going on under the impression he's done. The two sides had been having troubles recently, with a major setback being John Laurinaitis' call to go with Florida for a developmental territory - where WWE would start from scratch - instead of going with Booker's already established PWA, which WWE had been loaning wrestlers to. After they made the call to stop that, Booker went to his friends at TNA and booked them for his shows instead, which didn't sit so well with anyone backstage, but they couldn't say much having pulled WWE talent from PWA.
Booker is pretty much set financially and has wanted out of wrestling for a while. At age 42, he's accomplished a lot, and thanks to his hip hop store doing well in Houston, and his two wrestling schools up and running, there's really no need for him to stick around.