On one hand, I think they're not calling it yet because it's just further proof that this isn't some plot against him, he is legitimately being voted out. The numbers are speaking for themselves right now.
I'm giddy right now waking up with PA and GA flipping blue, but I'm also absolutely terrified for what comes next. We will face civil unrest and even more violence because he won't accept this. And they won't have a president to back them up this time.
Also, we owe Georgia to Stacey Abrams. I feel like this is her victory.
Edited to add: Tamieka Atkins, Helen Butler, Nsé Ufot, and Deborah Scott also share this victory.