It seems, in my experience, Wardens have a habit of sticking to only one prisoner when motivating and only rarely ever switch to a different prisoner or move to a non-Warden task, even when the prisoner they are stuck to has 100% motivation. I'm not sure if this is intended functionality, but it doesn't seem it. I would imagine that Wardens would motivate only prisoners in need of motivating and more onto other tasks if no prisoners need motivating