Because this is as much a political statement, and battle, as it is a personal dietary choice.

As crazy as it sounds, a certain segment of people love to change the definition of words. It is not enough to not want to eat animal products themselves, they also are not content to allow others to have these things to themselves unmolested by grotesque artificial imitations.

They want their non-thing to become the thing, replace it, and to the degree it disgusts and frustrates the normal crowd and impinges on their enjoyment of the normal version, the happier they are.