This is crap made by developers, I can make my own crap up. We're talking about an item that allows you to see the past, not like watching a video, literally experience the past as if you were there (as seen in the mq).
Who's to say there is a different kind of scroll that allows you to actually physically travel? I'm not to keen on this (my idea above wasn't about actually changing the past, it was just seeing it like the mq), but saying 'lore blah blah' is such a mundane argument to me when it's all rubbish anyway.
It's not like the laws of physics dictates the elder scroll can let you experience the past but not travel, it's nonsense.