Number 1 Neil and Carl weren't very close
Neil was appointed strictly to keep everybody in the family happy

Carl kept EVERYTHING in the family as much as possible

But most of all Neil passed himself over
If he wanted to be the boss he could have been
He just respected Carl's whishes as even though not close there was a lot of mutual respect

Also Remember Neil was in jail 74 and 75, in 75 Paulie was made acting boss
So he had all his bearings too from having been there in the spot for a year where as Neil was fresh from the can