It is not egg specific. The countries that wash their eggs have atypically strong standards for bacterial contamination hygiene in food processing. Many food products from Europe are prohibited from import into the US due to insufficient safeguards against bacterial contamination during processing. There is an entire business where Scandinavian factories process food from distant parts of Europe to satisfy US food safety requirements for export.
As a general principle, the US does not create exemptions in food processing regulations on the basis that the existing process is "traditional" or has a long history. Many other countries do.
In Europe, poultry vaccination against Salmonella is the preferred method. In most places Salmonella occurrences are exceedingly rare.
In general, Europeans believe that USA has atypically weak standards of food safety and that all the cases when certain kinds of European food are prohibited for import into USA on grounds of food safety are just cover-up stories, because the real reason is to avoid competition.
It is weird that USA has a phobia of vaccines even for poultry, because in this case there is no doubt that vaccines would have prevented the great financial losses caused by bird flu.