Evolutionarily speaking, our palms are very interesting. Across the primate family, it is clear that the palms are different from the rest of the skin on the body. It is believed that this is an evolutionary adaptation as primates use their hands quite a bit for getting around or manipulating tools and the skin there needs to be thicker and more resistant to injury. In a similar vein, as opposed to the rest of our skin, there are no oil glands in our palms.

To get to the point of your question, the cells in the palms of our hands and the soles of our feet do not produce melanin, the main component in skin that gives it color. This is why regardless of the color of one's skin, the palms are much lighter. Since freckles appear when melanin builds up under the skin, we don't get freckles on our palms or soles but can get them in other places where the cells produce melanin.

I don't know, but I suspect the reason is related to the fact that we have fairly little pigment on our hands to begin with. Think about the palms of the hands of black people: the skin on their palms isn't nearly as dark as the rest of their body. My guess is that the pigments that make freckles/dark skin just isn't produced in large amounts on the palms of hands.

Freckles are made of a brown pigment called 'melanin'. The cells in the palms of our hands and the soles of our feet don't make much melanin. Also, sunlight causes our cells to make melanin, so body parts that don't get much sun are not so freckled. I have freckles and brown spots on my face and arms and legs, but I don't have any freckles on the skin that's covered by a swim suit.