The night I was captured, Bellatrix, Snape, and You-know-who all tried to break through my Occlumency. You-know-who was enraged when they all failed. Realising that extended torture would likely damage my mind before my walls broke; they ruled out excessive abuse as the way to access my knowledge of the Order. You-know-who decided on prolonged humiliation. As the only Legilimens in his inner circle that could be trusted to carry out the task he envisioned, You-know-who tethered me to Malfoy with the instructions to "break" me.