Given that the human penis shows little variance, aside from a few cm in length, girth, and curvature, why then do we find such a large variance in the penetrative devices that women purchase for their personal use?

These devices range in length and size and resemble anything from a pinky finger to a horse-penis and in width from the same aforementioned pinky finger to a 2-liter soda bottle or more.

So how is it, evolutionarily speaking, that women came to prefer inserting a 2 foot object into their vagina as compared to a normal 4 to 5 inch human penis?