I think... that maybe they mean that it's too dark to see the bottom of the image and there might be an actual copulation going on in there and they want to avoid ambiguities like that? (Like, actual dicks and vaginas, just darkened, hk). The original book cover has her silhouette cut out and shown fully so I guess it's not the silhouette that's the issue but the darkened lower edge?
I have no idea, but that's the only reason I can come up with.
But that really is not that suggestive, tbh. I actually quite like it,
@K5Rakitan ! Pity it got rejected...