To explain, let's turn it around. Assuming you also live in the US, imagine a EU company would make the following assumptions that are common (to the point of feeling entirely "natural") in lots of European countries, but wrong in the US, and think about how that could impede you in varying business situations:
* There is only one time zone in a given country.
* VAT and other sales taxes are the same over the whole country (and therefore just included in the display price).
* Every debit card, credit card etc. has a PIN, and a common API to the bank for card/bank-specific verification.
* Every bank account is identified by IBAN, even across countries. Wiring money is always free.
* Decimal separator is universally "," and grouping is ".". (Bonus: Let's instead be in an Asian country where it's common to group digits by 4 instead of 3.)
* Dates are always either in order "DD MM YYYY" or ISO YYYY-MM-DD. In the case the year is omitted, "DD MM" is assumed and no clarification is ever made. Your appointment is 4.5., thanks for doing business with us! Sincerely yours, noreply@example.com.
* Car-related business: You have to be at least 18 to drive a car (and have spent the equivalent of thousands of dollars and many hours of mandatory theoretical and practical training). It is illegal to drive a car more than 2 years without a thorough inspection that forces you to fix even minor things (Autobahn speeds are dangerous), so old cars are uncommon. There are special enthusiast registrations for so called "oldtimers", but that still requires extra maintenance.
* Gastronomy-related: But you're allowed to drink beer at 16 (was at least the case when I was that age), anything else 18.
* You have to use/publish your real name, address, and other information mandatorily in a lot more situations (e.g. when hosting a website of any kind--imagine a business enforcing that for all customers).
You may find that if you want to do business internationally at all, you have to start caring about those things.