Here's why:

* Buzzers need a closed circuit to function: A buzzer operates by using an electromagnet. When an electrical current flows through the circuit, the electromagnet is activated, which causes a striker to hit a diaphragm, creating the buzzing sound.

* An open circuit breaks the flow of current: An open circuit means there is a break in the electrical path, preventing current from flowing.

* No current, no buzz: Without current flowing through the buzzer, the electromagnet won't be activated, and therefore the striker won't hit the diaphragm.

In essence, the buzzer needs a complete, unbroken path (a closed circuit) for electricity to flow through it and make it buzz.