One of the things that has set Marvel apart from its competitors is in their humanising of their superhuman characters. Spider-Man is a goofy, bullied teen; The Fantastic Four are an average bickering family, with added cosmic powers; the X-Men are hated and feared. Iron Man, on the other hand, was principally created as a rich arms dealer because Stan Lee wanted to troll hippies during the Cold War.
So how to bring him down from that mean spirited, satirical height, and into a "real" human character? Make him an alcoholic, duh.
Demon In A Bottle is considered a classic in the comic book canon, and it certainly helped redefine Tony Stark, his alcoholism becoming a permanent aspect of his characterisation that has been referred back to ever since. At the same time...it's a story about a drunk superhero. And one that ends with him pretty much conquering his drinking problems after a few weeks, which is hardly the most realistic depiction of a drinking problem.
Admittedly, it's a depiction of alcoholism in a guy who has a flying robot suit, but if you're gonna bring real life into your comic book, you've got to play by its rules at least a little.