Because that's not his name.
First, you don't translate names. Did anyone translate Nami into Wave? Fuck no they didn't.
Two, you don't translate names.
Three, if you're going to anyways because you're a fucking faggot, and I say that as someone who faps to futa, 3D lesbians, and fantasies of Komaeda and Slaine getting sodomized almost daily, then how about going for the food themed translation, like all Charlotte kids, that is Starch, rather than the common name of the flower that is confusing, not only because it refers to the whole flower instead of just the bulb, which is the part you eat, but also because it refers a Dog's tooth, which is a correct translation assuming you think erythronium japonicum and erythronium dens canis are the same plant (you fucking madman no it's not), but even if you do you should still not fucking mix up signified and signifier. Dogtooth is a western only reference to the shape of the bulb, which retards like you take as a sign his teeth are dog related, "OMG GODA", when really there is no such image or reference in the japanese name. In japanese katakuri reads and is homophonous with "off shaped nut" not "dog's tooth". Not to mention that his teeth are stylized and cartoonish enough to be any deepsea fish's or even an insect's mandibles.reeeeee
Anyways, you niggastream dick suckers won't stop even if I tell you to so I don't even know why I bother. Fuck you. FUCK YOU