Because the rule is "you touch it, you pay for it". No way around it.

Edited to add: come to think about it, the rules about ORD-DEL and the one stop direct flights between Europe and SWP, are very explicit, and one could argue that they apply to those particular cases, not to others. I still think 'touching' JFK will force payment for NA, but given that JL is a new OW member maybe this has not been tested yet (?), or at least I don't recall any reports here, one way or the other (?).

Maybe worth trying.