He earned it because when you look around, you see no one who's worthy. Good for him. I don't think Danilo was a great captain either. Suckatelli and Gatti aren't captain material either - one is too timid and mediocre, and the other is a Serie B level player whose grinta and heart can't disguise his blatant flaws and deficiencies.
No one on this current team is captain quality/material, but this is the Juventus we have become.