C. Moore is AWARE the left above image isn't REAL, but is there just to illustrate conventional rear shape. Kind of shape that'll win you Rear of the Year - twice! (he snorted). The shape of the glootiful muscle butt is, note, way different (see right).
More important, conventional butt is ALWAYS the same shape. Hard muscle butt is all changeable depending on the pose, the heels, the flexions, etc. And therefore is, even to C. Moore with his low boredom threshold, ENDLESSLY fascinating.
Every time she moves - a NEW butt! And better still, left gloot flexed one way, right flexed another... TOTALLY DIFFERENT shapes although SAME butt! Like two for the price of one (of your favourite product). What, pray tell, is not to like?
To summarise. One-shape fits all conventional butt is DULL, samey. Shape-shifting muscle butt is INTERESTING as forever reforming into glootiful new shapes.