Not admitting LCN existed or was criminally active was an older rule he chose to enforce. Is it smarter to plea nowadays? Of course, but guys hate Gotti because he didn't go by book and was out there in the public. Then they'll use this as example to show damage he did. This may have been one of only things he did by the book, not wanting Gambino family being acknowledged. Hate for one reason or the other, not just to hate.