Why do so many anti-feminists here accuse feminists of having penis envy?

It is just another way of saying what feminist are trying to do: make men more like women and women more like men. Since they are talking about women feminist mostly, they say this rather than saying these women find being a woman degrading and trying to be more like a man empowering. Hence, they want a pee pee (and all that comes with it, larger brains, larger stronger bodies, etc).