Why is midterm vote-counting taking so long in US' largest state?

Vote-counting in US' largest state by area, Alaska, takes longer because its vast geography makes ballot transportation difficult, as some areas are inaccessible by road. The state accepts mailed ballots for up to 10 days after election day, and those from abroad for up to 15 days, delaying the final tally. Moreover, in 131 precincts, ballots are counted by hand.