I can't fully answer that without trying to guess the who and why. My main guess, however, would be: Control. Keeping their faces covered is one thing they could control fully about the situation. If SP escaped at anytime, she could NOT ID them. If the police raided the place they were keeping her, she could NOT ID them. If they were planning to pass her off to someone else, she could not ID them. If they were hired by someone else to torture her for some revenge or specific message, she could NOT ID them. You get the idea. There could be many reasons they did not want to risk letting her see their face--even if their ultimate plan was to sell her or to kill her. They could not be sure their plans would not go wrong. One might even guess that SP is alive BECAUSE their plans went wrong somehow. I have no idea why she was abducted, who abducted her or what they planned, but their plans could have gone wrong or been changed by someone outside of their control. We just don't know. Keeping their faces covered was within their control. Maybe we should be asking instead what kind of abductors WOULD NOT bother to try to keep their identity a secret from SP? Perhaps we could rule out some theories thinking about it that way. IDK.