My impression, after viewing the documentary "Life Overtakes Me" some time ago, is that the answer to this question is: to avoid deportation by feigning mental illness.
What is most interesting is that it only seems to happen in Sweden, and to specific cultural groups.
I don't want to diminish the very significant hardships many of these immigrant/refugees are under. If telling my child to just lie still in bed, when the social worker comes by, allows my family to stay in Sweden instead of being sent back to Syria, I would probably do it too. If it was a requirement for a NG feeding tube to be placed in the child, even that might be an unpleasant but ultimately worthwhile sacrifice.
Resignation Syndrome seems to reliably and rapidly abate once the threat of deportation is removed. Is that because a massive stressor is removed and mental health can be regained? Or is it because a pretense can be lifted once the threat of deportation is removed?
I wonder why people think that there is must be a hard cutoff between these 2. You can create a very temporary OCD with "trauma" in video games. That's entirely fictional and voluntarily (literally done for fun) and yet you can clearly see the effects for a few hours after the video game session stops. It lasts longer when repeated.
So here's a theory: there's a long, very slow sloping grey zone between definite OCD and entirely faked and a million gradations between the two. The longer the faking lasts the more real it becomes.