At least one person I saw was in the stairwells on the way from a waiting area down to a train platform. I don't think passengers would want to sleep in the corridor between the gate and the plane at an airport, but you're right, perhaps it is only the locked door that is holding them back.
Now I am kinda curious why they were staying there if they were supposed to be guaranteed shelter. I wouldn't be surprised if the state failed to house them despite the law and that was the warmest place they could find or if the offered accommodations were unfit or dangerous.