#2 Accolades
Fans all over the world are already aware of his exploits. He has won most individual and club honours on offer. He may feel the time would be right to give the younger crop of players a chance to carry on his legacy. He has already accomplished the all-time top scorer honours for Portugal and scored the most international goals by a European player.
Also, he led Portugal to success at the 2016 European Championships so there remains little for him to achieve. The World Cup though remains elusive on his list of accolades. The next World Cup will be in 2022 and he will be about 37 years of age.
The Euros will not be such a huge motivation for him to keep playing tournament football if he wants to prolong his club career. Having already won the European title, he may feel that he has done all he could for his country.