The issue is not necessarily the background checks but the fact that you can be compelled by the state you reside in after the fact. For example the state could target known employees of GitHub after they are employed and checks passed.

I'm not suggesting any national correlation here. I suspect the same is true for Chinese and Russian companies too!

As for the defence sector it is not enjoying it, at least in Europe as the incoming staff into the sector are shrivelling up pretty rapidly.