Unless the "traditionalist" believes that Vatican II changed the eternal Catholic faith - which Vatican II didn't proclaim itself to do and no Pope since then has taken it as doing.
I don't see how that could be the case. If no change has occurred, then what can they be denying? No, Vatican II has effectively been interpreted by the mainstream as the foundation of a new faith and the SSPX is being attacked for not accepting those changes. Who cares if they deny a council if that council changed nothing? How many Catholics give any heed to any other council than Vatican II? The priests I have known have never shown any indication they thought any council ever existed outside of Vatican II, and further they actively deny numerous aspects of the faith which all those councils upheld. Are they ever in any trouble? Why is that?
Unfortunately we live in a post-Catholic church. Popes have no influence regarding orthodoxy any more. Our last pope made some suggestions about an optional private prayer, i.e. the Rosary, and all the Catholics leapt on it as a direct revelation from heaven which forbade any use of a traditional Rosary throughout the world. However, contrast this to the reaction of the "faithful," including bishops and priests, to the Holy Father's teachings and instructions on the liturgy? Crickets, if not open denial and insurrection. That popes, or councils, have not claimed to change the faith does not mean that the faith hasn't changed and that the hierarchy and curia are not enforcing those changes on others. The faith my children are taught in churches today is not the faith of our patron saints. It just isn't. We can say it is, but it isn't and we all actually know it. And when the SSPX refuse to play ball and continue as they did for centuries before we all somehow find ways to insist that they are the ones changing the faith, and not all of us. Too bad.
I don't see how that could be the case. If no change has occurred, then what can they be denying?
The changes that they and "Catholic" liberals falsely believe to have been decreed.