My guess is that to get a decent fare on a legacy carrier, you'll need to book it as either a round trip or open jaw ticket, not two one ways (even if on the same ticket/PNR). If you need to return to a different place in the USA, you'll need to come and go from the same city in Europe. Alternatively it could be cheaper to just purchase a cheap one way domestic ticket (but allow lots and lots of time for delays) between your two USA places.

Increasingly, many USA domestic tickets are priced on a one way basis (but some city pairs are exceptions to this) while TATL one way tickets are extraordinarily expensive.