Marketing.
And Ronaldo has been good. 29 goals + assists under Allegri's defensive system. He had 31 goals + assist with Real last season, a team much more attacking minded.
To put things in perspective, Del Piero never scored more than 21 in a season even at his peak. And Totti only managed to do that once in his career, otherwise never even reaching 20 goals.
Ronaldo does 21 + 8 assists at 34 years old in his first season in Italy and under a defensive team who couldn't even get the ball in the opposition's area in many matches..
Not good, great, considering everything.