Aver said:
They don't need Natalis to offer anything. With Natalis they can take EVERYTHING after war. They know that he is weak politician and that they can take whole diner instead of scraps that Radovid will throw them.
And as I already told you. It takes one nobles or a group to figure he can take everything when everyone else is busy to screw up the entire thing, because nobles are not the rational actors you think they are. And it takes a few nobles to decide they don't like how Natalis is not prioritizing defense of their own lands.
And it takes a few nobles coming to the realization that Natalis offers no guarantee of victory (or anything for that matter), whereas Nilfgaard can offer them much.
And Radovid is not so carrot guy as scenes where his troops are executing Temerian nobles showed. It was presented like Radovid is "obey or die" type of person. You can never know what will happen with you in future when someone like him is ruling the country. On other hand plenty of traitors had good life after they helped Nilfgaard.
He executed a select few people. He couldn't control Redania like that if he simply killed everyone.
Unlike Natalis, Radovid actually has carrots to offer. And they will think twice before betraying him lest the Order comes knocking on their doors. And Radovid has enough force and will to impose any military decision on them.
So if nobles were to decide between Natalis, who can't offer anything or scare them enough, or Nilfgaard that can offer them a lot, I suspect a number will pick Nilfgaard.
But if on the otherhand nobles had to decide between Nilfgaard, who can offer them something, and Radovid, who can offer them something as much as Nilfgaard and annihilate them if they dare to disobey (and they are in his turf), nobles are less likely to turn on him.
All that, plus the thing you keep ignoring. Political acumen. Radovid knows how to play the game, Natalis does not. Radovid can easily manipulate nobles to do his bidding. Natalis couldn't manipulate a sheep if his life depended on it.