A long way back, when the US was trying to sell the F16 around the ME and other areas, they originally insisted that all EW kit had to be integrated by GD back in the USA - purchasing nations having to provide EW pods and threat libraries.
Strangely enough the interested parties, many of whom had UK/FR/other pods had issues with this themselves - and with the manufacturers who had no interest in giving examples for the US to reverse engineer. Let alone the suspicion that a certain other nation, other than the US, might have back doors so they could operate without interference (in many senses of the word).
Labs in the US ensures that no US sensitive data escapes the USA, it also (being cynical) ensures the USA enjoys total access to all purchaser red and blue libraries and the synergies between them - whilst also enjoying the opportunity to - ahem - manipulate the resultant product, in the interests of national security.
I note the Israelis are being allowed to integrate their own EW equipment and datalink equipment. I note with interest the lack of mention of an Israel US laboratory.......
Panetta?s Visit Sealed F-35 Jet Sale to Israel - Inside Israel - News - Arutz Sheva
p.s. The US policy was relaxed when sales faltered. Perhaps it will do so again......