Here's why:
* Disturb is a verb, meaning to interrupt or upset something or someone.
* Disturbance is a noun that refers to the act of being disturbed or the state of being unsettled.
Here are some examples:
* The loud music caused a disturbance in the library.
* The earthquake caused a significant disturbance to the city's infrastructure.
* He was annoyed by the constant disturbance from his neighbors.