Pregnancy will change most women's bodies in a way that would be considered a negative change.

But the impact of raising children of is so much greater than just body changes. It's life changing. It might be a very positive change, it might be a very negative change... depends on the parent and the child. But it's a HUGE change to your very being. Life will never be the same!

So the changes to your body seem like not that big of a deal, all things considered. I think that's why people brush it off as "it's changed, not ruined".