Football is more than money. I don't know exactly what is going on within Al Nassr but they may have some dressing room problems, maybe the alchemy among the players is not good, maybe they don't like the manager... There are a ton of different reasons. And having someone like Ronaldo in your team may be both a bless and a curse at the same time because now he is more than a player, he takes decisions for the team.
Maybe that's the problem because some players would feel like he's giving more preferential treatment and gets jealous thereby causing dressing room problems for the team am just saying though cause I might be wrong, money is not a problem for Al-Nassr, they just need a coach that can manage the team and put them to order.