You may have hit on it - you said it's seen as "sort of weird" and "foreign". And how much sheep farming does the USA actually have? Furthermore, in the early days of the USA, the usual meat to eat from sheep was mutton, which really isn't a patch on lamb. It's older and tougher. Maybe that put people off when there were tastier things to eat. So mutton dropped out of the diet. Just guessing.
I'm British and it's very popular here. The Queen regularly serves Welsh lamb at state banquets because a) it shows off British produce and b) no religion objects to it, so there's no need to offer an alternative except for vegetarians. (She isn't much of a fan of fancy food either so what the guests are likely to get is roast lamb with potatoes and vegetables - ex-President Obama got that last time he did a state visit. Pretty much a very ordinary Sunday roast dinner as I would know it. A nicely roasted leg of lamb makes a good family dinner.)
The one thing people maybe don't like is the seasonality. Having visited a sheep farm I know a thing or two... sheep are seasonal breeders, they "get jiggy" as the days get shorter (around this time of year, in fact) and all the ewes give birth in January-March. As an auditor, I had to do observation of the farm's stocktake and when I went at the end of March, the lambing sheds were full of ewes nursing babies. Normally they have twins, who will come off mother's milk in spring just when the fields are growing new lush green grass for them.
If you want nice juicy lamb, the lambs have to be slaughtered at 6-12 months old (older than that and it's called hogget). So for half the year it just isn't available.
Our solution to this is our Commonwealth cousins in New Zealand. There are far more sheep in Kiwi-land than people, and ever since the country was found to be the perfect place to raise sheep, we've been importing their lamb to fill the seasonal gap - of course their seasons are the exact opposite. So what I will see in butchers or supermarkets is British lamb for half the year, and when that starts to get old, in spring and summer we get NZ lamb.