Are you a believer? If so, it seems a silly question to ask. If not, then I suppose an answer would be that to those of us who are believers in Christ, His sacrifice means more than can be expressed in words. You could ask the same of why anyone looks at photographs of friends no longer with around, or something along those lines.
I'm not a Christian, if that is what you mean. I still don't understand why you would want to watch torture. I understand looking at pictures of my grandparents while they were living, but surely not while they were dying or being tortured.
Then Jesus told him, "Because you have seen me, you have believed; blessed are those who have not seen and yet have believed." John 20:29
I don't need to see special effects to understand the real "Passion" of Christ.