I've read that Paul had had increasing oversight duties in the family since the early 70's due to Carlo's declining health and was for all intents acting boss from around 1975 if not in name.
It was said that carlos relationship with Neil was always a tenuous one and his ascension to underboss came about as a result of reconciliation following on from a faction of the family that did not support Gambino's power move on Anastasia.(several capos were murdered in the wake of A.A's murder including John Robliotto and Armand Rava who dellacroce was close to.)
The disrespect Dellacroce showed to another made member by having an affair with his wife, and supposedly children, would not have sat well with the traditional Gambino either.
I think when a figure like Dellacroce dies, sometimes the myth becomes bigger than the man and people think it would have been a cakewalk for Neil to just Take the family on Carlos death.
Don't forget that Paul would have had many around him at that time staunchly loyal to Gambino and by extension him, zappi, lombardozzi, the armones, the corraros and gaggi, all with hitters in their crews.
Having spent a good portion of the 1970's locked up maybe Neil just figured why rock the boat, I get to stay UB, I'm still making more then I can spend, Pauls proven in the past he can earn, why fuck up a good thing.