This is not simply a case of the sunk cost fallacy. Stopping the program now would result in a trillion dollars having mostly gone to waste. Most of that money

This is not simply a case of the sunk cost fallacy. Stopping the program now would result in a trillion dollars having mostly gone to waste. Most of that money went to the initial development of the program, and a comparatively small amount is now spent on each new airframe. Scrapping it right as the upfront costs begin to pay off as airframes are delivered makes no fiscal sense whatsoever. Operational F-35Bs have been delivered to the military since 2015. F-35As since 2016. Drones capable of fulfilling the roles the F-35 will do not yet exist. You'd be sinking a program where the overwhelming majority of upfront R&D has been paid off in exchange for starting a new program from scratch that may not deliver a drone for another ten, maybe fifteen years. Yes, today we could design and build a new set of aircraft with more modern capabilities. But with your logic, after fifteen years of R&D — just as units begin rolling off the production line — we'd be looking to scrap the program to start anew with whatever advancements those fifteen years in technological advancement might have unlocked. You're comparing a plane that's been in development for twenty years with a hypothetical drone with today's tech that wouldn't be ready for another fifteen to twenty years.