Wasn't this around the time that Gotti began to distrust Sammy The Bull, as we've been led to believe from various wiretaps and agents? If so, it's not that hard to believe that Gotti stopped feeding him literally everything he knew about.
Mobsters badmouth each other all the time. Rotondo was hit in January 1988. Gravano was made underboss sometime in 1988 or 1989. Gotti was planning and discussing hits with Gravano up to the end. The Garofalo and DiBono hits both went through Gravano in 1990.
