It's a popularity contest

To some extent, yes, but you still need to be exceptionally good to be considered on the shortlist. It being a popularity contest doesn't completely and absolutely nullify the prestige of the award. There's a good reason Messi and Ronaldo are the only winners of it in the past 8(?) years, because they're quite clearly a level above everyone else. Just because you feel someone else should have won it in a couple of years, doesn't mean the reward is entirely inaccurate. It is still accurate to a good extent. 2010 and 2014 were controversial, but what about all the other years? Would you disagree with the winner?

How can a player who hasbt won the world cup or champions league be considered the best

Trophies are team based awards, not individual. E.g. a striker scores 50 goals a season but his team wins nothing, while another striker scores 10 and wins the treble. That doesn't mean the latter striker had a better individual season. He just had a better team surrounding him.