According to Chris Broussard, the Cavs had a deal in place that would have sent Irving to Phoenix for a deal that included Eric Bledsoe and Paul George, and though the deal didn't go down, Irving thought that James must have signed off on it. This was apparently the "final straw" for Irving, who then went on to request a trade of his own. Kyrie is now likely to stay after finding out LeBron does not want him gone
MOD EDIT - Edited title, adding the Broussard segment from The Herd (from earlier this week):