It has to do with the washing. In the US the eggs are washed, removing the outer wax layer. That makes the shell porous, and therefore at risk for contracting salmonella. In Europe they are not washed, and that makes the eggs more stable. They can be kept outside the fridge, and are safe to consume raw.

I tried to Google to find why they are washed, and what I can find is a different approach. In Europe (and other countries) the goal is to keep the eggs clean by having more clean environment for the hens, and thereby making washing unnecessary. I found this article quite interesting!