Why hasn't AP called the Alaska and Mississippi Senate races yet?

The Senate races in Alaska and Mississippi, which are yet to be called, will determine the strength of the Democratic majority. Both contests have narrow margins with votes still outstanding, even as the scale of Democrats’ victory across the country comes into focus. The Mississippi Senate race is very close and several thousand provisional ballots are still being counted. In Alaska, no candidate has yet secured the 50% of the votes required in the state's ranked choice system.