Tag definition of vore: The gender of the one getting eaten determines if the tag is placed in the female or male namespace. Why can't people be bothered to read the definition before tagging?
People know the tag definition, it's just that nobody cares about the gender of the one getting eaten. According to our desires, using them to identify the one doing the eating makes more sense. Hence, many people use the tags like that instead. But with how people are split between using the tags how they're meant to be, and how they should be, the gender has become pointless.