I'm not a fan of the new DL $$$ F&B options, but most of the other lounges aren't membership lounges. The only way in is J/F ticket or high elite status (which is generally much harder to earn outside the US). The SkyClubs, OTOH, are membership lounges that happen to comp access for international J passengers.

That said, DL could easily fix this by comping $$$ F&B options to anyone on a J ticket (and maybe even throwing STE+ on an international itinerary a freebie or two) while continuing to charge for day pass, Amex, and even regular SC members.