Here's why:

* Scalar quantities have only magnitude. They describe how much of something there is.

* Vector quantities have both magnitude and direction. They describe how much of something there is and in what direction it's acting.

Luminous intensity measures the amount of light emitted from a source in a particular direction. It does not have a direction associated with it, only a magnitude (measured in candelas, cd).

Think of it like this:

* You can say a light bulb has a luminous intensity of 1000 cd, but you can't say it's "pointing" in any specific direction. The light is emitted in all directions.

While light itself travels in a direction, luminous intensity is a measure of how much light is emitted, not the direction of the light itself.