Copa America is a tough tournament. And since Messi's been playing in it, it's been won by Brasil twice, Chile twice, and Uruguay. If it were just a matter of beating Brasil, they would have won it already.
So, while Messi has been shit on for damn near his whole career for not winning anything with Argentina, when he finally does it and is undoubtedly the best player in the tournament, it's suddenly "so?"

Lewandowski should have gotten the trophy in 2020. That's clear.
But in 2021? Based on what? Winning the German league? C'mon.
Based on goals? If that's all it takes then Messi should have 2-3 more Golden Balls than he does. Because he was the leader in goals+assists in several years when he didn't get the award.