Do you actually have a source for this? Like, a medical one?
Men & women stock fat differently, women tend to store their fat in their hips, buttocks, thighs, and lower abdomen which is more visible (men store fat around their internal organs mostly) meaning that to have visible abs they have to lower their fat percentage even lower than men which tends to be less than is healthy.
Of course women can have visible abs without being unhealthy, like you say plenty of athletes do but when you actually look it up they tend to be visible but not that much, like they don't have crazy 6 or 8 packs sticking out most of the time. Googling "women athletes" shows this pretty clearly (unless it's some action shot, obviously flexing your muscles is going to make them more visible. Case in point; those pics you showed).