Apparently one aspect has to do with the inevitable result of a what a stealth fighter is: it can deploy weapons far further than it can see. So without comlinks with intelligence from a specific satellite system, it loses half its features.

Second for the on-board radars to evade detection they need to be reprogrammed with the latest updates regularly. Not so much because the programming has a kill switch but because otherwise "adversaries" could still turn out to have rockets that can home in on an F-35.

And even in the case of the US, you don't have to shoot down that many F-35s to get them all.