I think it goes to the most popular player that wins the biggest trophy. But the player needs to be popular and hyped by media. Thats why a Ribery or Sneijder didnt win. If for example Real win cl again it goesto Ronaldo again its that simple. If Bayern win it goes to lewa (unless he is completely invisible). If France win the wc it goes to Pogba, same with psg/Brazil for Neymar.
But if for example Germany or Spain win the wc it wont be 100% that one of their players win. Unless they start a campaign for you like canavarro or what they tried with buffon last year.
Even if for example Real win cl and Spain win the wc it wont go to Isco/Ramos but to Ronaldo again due to his popularity.
At this point its known as the messi vs ronaldo award. So they will be compared first and it goes to either of then depending on the year unless a popular player wins something more prestige.
2013 was a total fraud year where Ronaldo got it out of pity. 2010 Messi would not have won it in the current (old) system. 2012 they got a campaign going based on his 91 goals.
All the other years cl already sealed it for Ronaldo.