In the past, Sting and the WWE have come very close to an agreement, but a primary factor which stood in the way was Sting's questioning of the WWE product. At the time, the WWE product was far more racy and didn't click with Sting's Christian lifestyle values. Now with a more PG product, that is no longer an issue.
Sources close to the situation feel that Sting also feels that it's "now or never" for his opportunity to join the WWE. Additionally it is believed that the WWE is expected to use Sting as the figurehead of the WCW brand that they will be heavily promoting on the WWE Network.