Batman is often portrayed as a sad and brooding character because of his tragic backstory. As a child, Bruce Wayne witnessed the murder of his parents, which had a profound impact on him. This traumatic event fueled his desire to seek justice and protect others from experiencing similar tragedies.
Batman's sadness also stems from the immense responsibility he feels as Gotham City's protector. He carries the weight of the city's crime and corruption on his shoulders, and this constant battle against evil can take a toll on his mental and emotional well-being.
Furthermore, Batman's no-nonsense, serious demeanor is a deliberate part of his crime-fighting persona. He believes that projecting an intimidating and unyielding presence helps to strike fear into the hearts of criminals, making them less likely to challenge him.
It's important to note that while Batman may appear sad and rarely smile, he is driven by a strong sense of justice and a desire to make the world a better place. Despite his somber exterior, he remains committed to his mission and the protection of Gotham City.