You don't know Sanji fans exist because you live your life in a bubble, trapped like a goldfish in a bowl. But in the presence of Sanji, you're slowly confronted with the reality that no, your miserable state of squalor is NOT the norm or anything worth aspiring to. When you see something categorically better (i.e. Sanji) then all you can do is lash out, throw a tantrum and try to demean and bring it back down to your level.
Success breeds jealousy. I'd be wildly angry if I were a Zoro fan too. But as a Godji fan all I can do is shake my head and laugh.