I'd wager that the main reason is that the concept of transit is completely foreign to US airports. Even if travelling to a third country you need to go throug

I'd wager that the main reason is that the concept of transit is completely foreign to US airports. Even if travelling to a third country you need to go through immigration, customs, re-check your bags and go through security to get to your connecting flight. You cannot check your luggae through. A process, which is possible if you fly through virtually any other country. I wonder what this costs US carriers. For example: Flying from Zurich to Lima would be logical, connection wise, via Miami, Atlanta, or even New York. But I rather fly via Amsterdam or Madrid to save myself the hassle and the anxiety of missing my connecting flight due to innane, unnecessary procedures.