Sex dolls, like robots and mannequins, all suffer from the same problem: The dead look. The more they try to make them look real (face, eyes, lips), the more our minds see the differences. This is called the Uncanny Valley.
Humans have no problem falling for things like teddy bears. We look at them and think they are instantly cute and apply a "life" to them. Kids talk to their dolls for example and can easily imagine them as real.
Dolls and other things that are supposed to look "real", fail when there is not enough detail. Things like skin texture, muscle under the skin, natural movement, eyeball moistness, and the normal random movement of eyes, skin, expression and bodies are all visual cues that tell us this is a living thing, vs a dead thing.
The same is also true in computer graphics. We easily emotionally identify and bond with both traditional cartoons and computer generated cartoons, but feel disconnect when CG is used in a way that somehow does not offer full realization to the person. For example:
Same thing happens in dolls:
When sex doll makers can get past this, they will have a crazy selling item on their hands. Until then, I think only the most lonely or most desperate will ever buy one.