Eh? The US is the opposite of "mostly flat". And large swaths of the mostly flat part have low population density. The country is also very regional with considerable local diversity in what is produced and available locally.
The US produces a lot of very local artisanal products throughout the country that don't travel very far that are based on local tradition and history. That's been true everywhere I've lived in the US.
Eh? Most of the population lives in the Atlantic coastal, Gulf coastal, and Midwest plains. Only a minority of Americans live in places that could be considered "mostly mountainous", methinks.
Even Denver, the most populous city in (arguably) the most mountainous state, is actually a Great Plains city.
I've read that before the Transcontinental Railroad, it was cheaper and faster to get to San Francisco from a port in China than from St. Louis.
The reason we have less stuff like this in the USA is due to geography. We are a mostly flat country, rather than being mountainous or separated onto different small islands. Because of this, products produced via economies of scale can outcompete higher-quality artisanal products.