#3 He has broken all sorts of records

Look at Real Madrid's record books. Since Ronaldo came to Real Madrid, he has broken/created a lot of records. That's how he has actually dominated every Los Blancos legend to pass through the doors at the Santiago Bernabeu.
He is the highest goalscorer in Real Madrid's illustrious history. Also, he holds the records as Real Madrid's highest goalscorer and assist-maker in La Liga and is the highest goalscorer and assist-maker of all time in the Champions League.
He holds the records for being the fastest player to reach 50 and 100 league goals for the club and he is the fastest player to reach the 200 and 250-goal benchmarks for Los Merengues. Add a chunk of other personal and overall records and you know that there's nothing left to prove for the number 7 at the Bernabeu.
Joining any other club, say Manchester United or Paris Saint Germain, would open up new possibilities for setting milestones, something that he loves doing more than anything else.