Because the actual witnesses viewed those as modest accomplishments. Oda buys heavily into goodwill, or the commercial idea of karma. Zoro:
- swore to avenge someone who showed him kindness and was butchered in front of him
- gave up a supremely valuable treasure, his own sword granted in victory
- took Hakai on behalf of those who will go on and keep fighting
- opted to take double the pain he accumulated in order to get another chance to fight
It's ridiculous and disappointing to think this won't all pay off. Tbh I don't even see him wasting time with King so I don't feel like there's any greed in asking for him to kill Kaido.