Commercial American eggs are federally required to be washed and sanitized before they reach the consumer. EU egg marketing laws, on the other hand, state that Class A eggs – those found on supermarkets shelves, must not be washed, or cleaned in any way.
The reason EU forbids eggs from being washing is to encourage healthy practices and cleanliness in its farmers. The thinking is that if an egg is dirty, no one will want to buy it.
In the US, the approach is that cleaning the eggs makes them safer, which is true. It also increases the risk of contamination if eggs are washed improperly.
More here. It's way more interesting than I thought.