My guess is either (a) they're hand-counting all the paper backups, and/or (b) campaigns are chiming in and confirming or disputing results before the IDP makes

My guess is either (a) they're hand-counting all the paper backups, and/or (b) campaigns are chiming in and confirming or disputing results before the IDP makes the result public, which means more time for folks to weigh in and more fact-gathering before the public knows the results. And that while this wasn't the plan, the initial things going wrong caused such distrust in the process they felt this was necessary.