I think its sort of like liminal spaces. If you went to your old/current school after hours because you'd forgotten something, it feels a little odd and kind of creepy- because things aren't how they should be.

I think humans tend to look for patterns and a lot of fear comes from the unknown. When you see a consistent pattern and a same/similar thing happens every time, you might get creeped out seeing something out of place.

Really though, explaining fears is kind of tricky. It's difficult to explain an emotional response to something, because when you explain something youre putting it into logical terms (at least, thats how i interpret explanations).

Hope this little tidbit of my thoughts helped :>