It's often -- but not always -- faster to create.
And sometimes, it's the right choice for the story. My previous comic was B&W, and if I were to do it again, I'd either do the same thing or use very limited colors (e.g. monochrome with spot colors). Definitely not in full color. It's kind of like how B&W photography is still done these days for artistic reasons.
My current comic, on the other hand, benefits greatly from the full color palette. It has a visually exciting world to show.