Killing the son or close relative of a made member, even if he's just an associate, is a very delicate matter. Usually it has to be okayed by someone who is a lot politically powerful than the family member or if the family member associate fucks up so bad that the made guy can't protect them.

Junior was a Gambino associate (in 1983) and Gotti's son, so it would it would be a Gambino matter to handle, it would been seen as meddling in Gambino family internal affairs if he went outside of the family to get help. Unless there was a reason for them to gain something, another family wouldn't want to touch it with a ten foot pole-more trouble than it's worth.

If Carneglia was under John (IRRC), he could have made a sort of appeal to Dellacroce about it, but that would have been a death sentence since Dellacroce and Gotti were so tight that Dellacroce would have told Gotti about it and that would have been the end of Carneglia. It's not polite to ask permission to kill you capo's son, made man or not. Gotti could have eliminated a threat to his son and got an excuse to take over Carneglia's operations in one stroke.