The issue with not calling it, is the perception it allows and the wasted time it provides

[StarfishSaver]

18. It's not exactly that, but you're close

I don't think they're afraid to call it while the challenges are pending. But the challenges are affecting whether certain ballots should b counted and that is slowing down the count in a couple of states. And that can affect the projections.

For example, the courts have ordered Pennsylvania election officials to segregate the ballots received between November 3 and November 6 because there is a dispute as to whether those ballots can be counted. It's likely that those ballots won't make any difference, but the state won't know until they count the other ballots and know the numbers and the margins. But as long as it's still possible that those ballots could make a difference to the outcome, it would be premature to project a winner.