We say "every vote counts," but in the last election, many of the precincts reported a winner with only 30% of the votes having been counted (as reported the following morning on multiple online news outlets). Continuing with this could lead to a future candidate conceding the race in error.
Delaying the reporting of the result until 90% of the national vote has been counted has many benefits, even if it means results are revealed the following day:
-It would result in more turnout (the west coast wouldn't be able to rely on eastern results).
-It would focus the media to the issues instead of to distractions such as states switching color as votes are counted.
-It would reduce the possibility of the wrong candidate conceding.
-It would restore the importance of each and every vote.