I'm not sure why lamb isn't eaten more the United States; I adore it. But often people will just blurt out, "I don't like lamb." In some other parts of the world, lamb is precious, but more common than stateside--as is goat. It doesn't answer the question about why so many Americans "don't like" lamb; I think they just haven't had much of it and what they have had as been poorly prepared. I wish they could have some stew...
I rarely had lamb growing up--and, if I did, it was a tiny lamb chop with some potatoes and peas prepared simply to showcase the sweet bite of meat. Of course there was mint jelly. This may have had something to do with living with in 25 miles of the Chicago Stockyards, or simply in the mid west where beef was (and is) king. Maybe it was southern-born parents cooking up north. Maybe it was cash.