At all times relevant to United's change in approach re: JFK, it had, and continues to have, access to capital to fund major strategic expenditures. A JFK slot portfolio would absolutely fit into that category. If COVID showed us anything, it's that the markets are willing to support virtually any reasonable proposal by the airline industry to lever-up. And no, United's JFK pullout this time around is not at all about cost savings. I'd wager United probably lost money on nearly every JFK departure it flew since resuming service (if not that, then in the aggregate) and it was publicly willing to continue to absorb losses as it attempted to build a larger presence. To date there hasn't been any ability for United to acquire slots in a meaningful way, outside of random late-night slot pairs that are useless for transcontinental business traffic (see Norse, Air New Zealand), and when the slot waivers expire at the end of the month, United is simply out of luck.

I can assure you that major slotholders like American, Delta and JetBlue have no interest at all in "selling" a material number of slots to United so that it may relaunch services that would be directly competitive with some of the aforementioned carriers' most successful JFK markets. For the same reason I mention above, not a single one has needed to resort to asset sales, especially those with positive future cash flows (like JFK slots), to fund long-term viability. This isn't a situation like Pan Am or TWA faced in the 80s and 90s, where firesales of crown jewel assets were the only path to cling to life.

So, I understand your point in the theoretical (everything has its price) but in a real-world, practical sense, United is in search of a unicorn. Are you suggesting that United should be making what amounts to a hostile takeover of AA, DL, B6, etc. for the JFK slots? Not realistic. There's no market for what United is seeking. Petitioning in the media for some allocation of slots during an DOJ proceeding with two incumbent JFK carriers is a bit desperate, but they don't have many other options.