Things are not always so simple like that. In some ways you can say it was a money question in others you can't. The previous season Ronaldo was promised a better and upgraded contract. In December Florentino was flirting in public about Neymar while Ronaldo was being awarded his 5th Ballon d'Or. Not comments are needed here. On January they present him a contract with the same value and only added extra as bonuses, so he would need to actually win UCL and get Ballon d'Or to get in full the value they promised before. Then they left him alone with that tax problem that he assumed. While Barça all backed up Messi. All this years he's been putting the sweat, he's been putting the bread on their plates. He decided it was over.