I dunno why people are hating the fact MC died. He didn't die because of the rule change, he died because he gave up complete control of the notebook, and since Ryuk himself will always kill the first user of the notebook, he killed the kid.
The rule change was there so he wouldn't have to be stuck in some vault forever because he had to go back to the Shinigami Realm, and probably also because selling the notebook makes the whole thing more boring for him. He goes to earth to see the chaos and greed that comes because of a book, not countries sucking eachother off with debt and finances while some zoomer profits and no one dies.