It gained popularity as a bartender's drink
The century passed, cocktails fell out of favor, and ingredients were lost. Then, after the turn of the millennium, we were hit by the cocktail renaissance. New gin distilleries started popping up in England, the US, and beyond. Vermouth saw a resurgence with increased variety and quality. The Negroni started appearing on a few cocktail menus, then many more. And now we have an international week to celebrate it. What, exactly, happened?
Like many other trends and fads, the drink started as a bartender favorite, then spread to consumers. At the time of its initial rise, most cocktails were either dark and sweet, like the Manhattan, dry and bracing, like a martini, or citrusy, with whiskey sours, margaritas, or the definitive drink of the '90s, the cosmopolitan. When the Negroni resurfaced, for many it was the first time a drink's primary flavor was bitter. It opened up the doorway to a new approach to cocktails. Both bartenders and bar-goers were thirsty for a new style, and the Negroni provided.