#3 Lack of striking options
Apart from Cristiano Ronaldo, Paulo Dybala is the only other recognised striker in the current Juventus squad. Many times last season, the duo bailed Juventus out when the team struggled to get goals.
Andrea Pirlo has been expectedly looking at getting some striking reinforcements, with the likes of Luis Suarez and Olivier Giroud among others being linked with the club, and one can understand the gaffer's logic as he wants to ease the pressure of Ronaldo and Dybala.
Both players had potent seasons last term, but Juventus are genuinely short of options up front as Dybala prefers to operate in a more deep/false 9 kind-of role. In such a situation, Cristiano Ronaldo has to play as the central striker.
#4 Cristiano Ronaldo's prowess as a centre-forward
Cristiano Ronaldo scored 311 times in 292 games in the La Liga. Let that sink in. It is a truly phenomenal record that helped him climb to second spot in the all-time list of goal-scorers in the Spanish league. It is safe to say that Cristiano Ronaldo's goal-per-game ratio in that league won't be overtaken soon.
As the Cristiano Ronaldo-propelled Real Madrid won one Champions League title after the other, the Portuguese maestro showed that he can probably be the best centre-forward in the game when on song. He could be the fulcrum of Juventus' attacks as well if he sticks to being a centre-forward.
#1 Cristiano Ronaldo's current attributes suit a striker's role
Cristiano Ronaldo is probably the most potent header of a football. His jump, anticipation and power have seen him score of the best goals of his career with his head. With his speed waning, his efficacy as a winger will decrease, but his ability to find goals will help him stay one of the best goal-scorers in world football for years to come.