Adding a prison would create a lot of RP a lot of people serving time just scroll on their phones and overall boring.
Imagine this you are serving a 30 year sentence and you are in prison creating connects, trading stories about your arrest and lifting weights to gain strength . You see people you are hostile with and create fights, maybe craft a shiv to take him out.
Adding a prison MAY take FPS but it doesn't have to be a large prison this would benefit the jail community by actually adding RP to it.