The correct answer is state law required a recount when the results were close
According to Florida state law, a recount is obligatory whenever the difference between two candidates is small. Since it was fewer than 2000 votes, around 1700 to be more precise, an automatic recount had to be done according to the law and it fell to a 900 difference. Because the recount decided who the president would be, they did a manual recount.
