Also, prior to the election, there was a non-trivial amount of fear about protests/riots/violence, particularly if the election was close and disputed.
While we don't seem to have avoided a close election, so far it seems like society as a whole is doing okay sitting and waiting for the final and official outcome. So that's an uncertain risk which is appearing to be less likely than it was perceived to be a week ago.
Edit: But as MDM said, no one really ever knows why the stock market does anything. We can just come up with a set of plausible potential explanations.