User blog comment:Lord Dalek/Am I the first to think this?/@comment-3501448-20120416060051

I think the wall only covers events to that point in history because Alduin is considered to be the harbinger of the endtimes, and thus the wall is more apocalyptic than historically accurate. That's like saying the world will end this year in december because the Mayans ceased recording time.

It's just a matter that whoever created the wall saw Alduin's rebirth as the end of the world, which the Dragonborn stopped.