From what I understand,Gotti believed that he would win on appeal,or even get a pardon. He really felt that the public loved him so much that he could cause a groundswell of protest that would result in pressure on the Government. Even Sammy thought he was nuts when he started talking seriously about getting together enough cash to bribe the President and get a pardon.

Bottom line,his delusions about his own press led him to believe that his conviction would be overturned. When the day came,(if it ever did) that he accepted the fact that he would die in prison,his final f*** you to the Feds was silence.

The Feds might not have even needed anything from him that they hadn't already gotten from the Bull and other snitches.
I think that in Gotti's case they took it personal,since he made them look like goofballs for so long.The thought of making his time easier by turning him was probably not even a thought.