I wish I could find mutton easier! I've always loved "Gamey" meats. I've mostly only found mutton at Halal butchers, and only some times. Rarely at extremely "high-end", bougie butchers, and very expensive.
I (American) think the gamey taste is exactly what most American's do not like at this point. Any time lamb, elk, bison, etc. are an option (usually at a restaurant), people voice complaints about gaminess and order beef (in my experience/social groups). It doesn't explain why it wasn't part of our food options we grew up with as this article is trying to explain, but I think it's why it's a hard sell today.
I will get lamb occasionally at a restaurant and about half the time it's too gamey for me (and I then regret my ordering decision). We also don't eat a ton of curry dishes where the seasoning and spices can maybe mask or enhance that flavor (I don't know what it does but assuming more flavors results in less noticeable gaminess).
It seems that it's difficult to introduce new meat sources to the market. Bison has been trying hard the past 10-20 years and it's a really good beef-like meat for burgers/steaks but still quite rare to see at a restaurant much less a grocery store.
There is still a big difference from grass fed beef and bison and the leaner meats like elk and venison have a much different flavor and they seem more difficult for me to cook right. I love venison, for example, but I don't always nail it. And it usually helps to spice it or sauce it.
I think bison has become a lot easier to find recently in grocery stores, especially the higher end ones. I enjoy the flavor and I would like to see more pastureland in the U.S. return to bison ranching.
Move to Michigan! Our large Middle Eastern and African population ensures you'll always be able to get it from any stand alone butcher and very often at your normal grocery store.
