gogtrial34987: Hover over them as they're waiting at that door. They will have a legitimate (non-escape) reason for wanting to go through that door (usually having to do with prison labour), and will have pathing which decided that the swiftest way to get to that goal was via the "outside". Of course, then when they're outside, they notice "hey, I could escape!" and make a run for it.

So, the solution to this is to make certain there's a more efficient route inside the prison to their destination (fewer doors, faster floors), marking zones as "staff only" and/or "access only" to prevent prisoners from going there, and worst case, just building a fence around the very outside of the map with no 'destinations' outside it, so prisoners won't have a reason to try and go there.