They think that "thicc" can exist without the pockets of fat everywhere. Without the sagging breasts. Without stretch marks on their stomach. Tbh I think that anime targeted at kids/preteens do show somewhat realistic body proportions for Japanese girls of that age. In Sailor Moon the girls are supposed to be 14. When you watch Serena/Usagi in normal street clothes, it's apparent she doesn't have the giant boobs or curvy hips she has in her Sailor Scout uniform; it's just that, a uniform that gives the illusion of those features. In Pokemon, especially the latest renditions, they have the bodies of children/pre-teens. In some adult anime targeted at women, like Nana, beyond the larger heads the bodies themselves aren't "unrealistic."