...or are you asking because you know every designer that's worth anything will explain it just to show off their knowledge?
They might say because vector graphics can be scaled up to the size of a mountain without losing quality and the file size wouldn't change? ...or maybe they'd say it's because it would always ensure clean, crisp lines and shapes and the vector information contained in the file also contains color information used for printing spot colors, so whichever print house you send it to in the world will be able to reproduce the logo perfectly by printing the assigned spot inks? ...or will they give you one of a hundred other reasons why vector is ideal?
An artist is not paid for his labor, but for his vision.