For the same reason the safe money says your school, like mine, taught you he was probably a drug addict who hated everybody and had no friends and drank himself to death.
Because by some wacky mix-up, somehow the right to legally execute Poe’s literary estate and therefore the public image he carried following his death was transferred to a dude who openly and without shame hated Edgar Allan Poe.
Due to some legal mumbo-jumbo and trickery, this dude Rufus Wilmot Griswold somehow managed to get the rights of literary executor to Poe’s estate from his aunt (which she didn’t technically have the power to give, that power remained with Poe’s sister), and he and Edgar Allan Poe hated each other SO MUCH in life, that after he died, this asshole published a memoir of Poe’s life in which he was totally demonized.
Rufus Wilmot Griswold is one of the most successful character assassins of all time. Because of him, schoolchildren are taught that Poe was a depraved misanthropic lecher who lusted after his underage cousin, was never sober, and died of drinking too much even though all of those “facts” have been discredited. Poe was a shy and reserved, though generally personable, man who married his cousin so to establish legal guardianship and provide for her financially.
He was also apparently a total lightweight who got tipsy after a few sips of wine, but occasionally drank socially or when feeling particularly down. His doctor insisted there were never traces of opium in his system. Poe’s friends insisted that he was not an alcoholic. At the time of his death, he had quit drinking, and the idea that he was one was heavily promoted by other members of the Temperance movement who claimed his death was a relapse as a cautionary tale. The most commonly accepted theory as to Poe’s death is that he was abducted, drugged, and beaten by political agents who forced him to vote for their candidate, changed his clothes, and then forced him to vote again and again to stuff the ballots.
Anyhow. This is why you should evaluate the validity and agendas of your sources.