

I strongly suspect that this was all by design. If they jail them in US prisons, it’s very easy for them to be released. When they’re being held by a foreign government, it’s very difficult to force them to release them, especially when they know the president doesn’t actually want them released in the first place. I’d even wager there’s an under the table agreement that they won’t release them, even if pressed.
You might also enjoy The Shoulders of Giants.