[learc83]

>Linguistically and culturally, the US has massive differences within it.

Culturally: Compared to a small European country--yes. Compared to the EU-- not at all.

Linguistically: 92% of the US speaks English. Within that group, dialectical differences are relatively small even compared with much smaller countries like the UK.

African American vernacular english is the only major dialect that is different enough to really impact communication, and even then, the majority of African Americans (and speakers of other smaller regional dialects) can easily understand the prestige dialect.

[cuboidGoat]

Although many of them are only represented by relatively small populations, the US has a much wider range of languages and language groups than Europe, as it has the languages brought from Europe, the creole languages from the slave trade, as well as the remaining native languages.

[learc83]

>relatively small populations

That's the relevant part for the purpose of calling it a single market.

>the US has a much wider range of languages and language groups than Europe

Unless you're talking about Indigenous languages with less than 10k speakers, that's not true because Europe has experienced significant immigration over the past decades.

If you are talking about those languages, it's irrelevant because fewer than 150k people speak them, and only a few thousand aren't also fluent in English.