Because she doesn't really put effort into her flops, they aren't some spectacular radio geared tracks with a big budget video and heavy push. She literally lets the label issue them out to radio way too late, doesn't give it promotion or a video at times like Right Now. I think her only true flop is CKB because that was seriously pushed and should have been huge off the heel of three big hits but again Cheers clearly should have been the 4th LOUD single, it peaked at #7 without a real video and it was the sixth single.
Also to that last point she has many songs she doesn't touch and they blow up like Break It Off, big top ten hit with no video or promotion. Cheers, Pour It Up etc. Stay got a basic ass video and little promo, (SNL was before it was a single) and it is now a signature hit for her.
So in final and I will shut up, she is effortless. People know better than to count out queen of music and versatility