>>212454800
because the protagonist is who the audience view the story through.
often times this causes them to be hollow. if they behave too oddly, or too ambitiously, or too differently or too erratically. It risks the audience's immersion breaking.
the villains and antagonists aren't as constrained which almost always allows more characterization and this characterization is what makes them so cool, it's what makes them interesting, it's what makes them memorable.
sometimes the villains become the main drivers of the story. which only adds to the factors that make the audience enamored by them.