That's because skin color breeds true. Eye color doesn't.
Look around you in America today at the various shades of skin color, from transluscent white to pitch-black and everything in between. Skin color gets more easily mixed than eye color.
I see your point, but I can't resist giving a biology lesson here. (This stuff fascinates me.)
There are several different genes controlling eye color; some are dominant and some are recessive. You get one gene from your mother and one gene from your father. Call the brown-eye gene B and the blue-eye gene b. Suppose both your parents have the combination Bb, i.e., a brown-eye gene and a blue-eye gene. Now brown-eye is dominant and blue-eye is recessive. So if your genetype is Bb, you have brown eyes. So look at the child of these parents. There are four equally-likely outcomes: BB, Bb, bB and bb. The first three outcomes result in brown eyes; but the last outcome gives you blue eyes. So two brown-eyed parents can have a blue-eyed child. Now, to my point: Suppose both parents have the genotype bb. Then the child is guaranteed to have genotype bb. So two blue-eyed parents will "breed true" in producing only blue-eyed children. (Of course, the truth of the matter is more complicated, since there are other eye colors running around that might be recessive to blue.)
The really curious story about genetics and color concerns calico cats. It turns out they don't breed true. To obtain a calico cat, you must combine the "tabby" gene with the gene for black hair. But both of these genes occur on the X chromosome, so to get both, the cat must be female. (Females have two X chromosomes but males are XY.) So all calico cats are female. But not really -- one in every 3500 calicos is male. Turns out that such cats have genotype XXY, they have an extra X.
What does that mean ?
I have known so-called "black" families which had children with characteristics of skin, eye, and hair clolor ranging form blue-eyed, fair skinned blondes to brown-eyed, dark-skinned black-haired children. Same mother and father.
Eye color doesn't.
Eyes are light or dark.
My children's eyes changed from bright blue to green-hazel as they got older.
Hair color can change with age as well.
I was a platinum blonde toddler, then went to brown.
Now that's changing too !