Here's why:

* Surge protectors are designed to handle sudden, high-voltage spikes caused by lightning strikes. They divert this excess energy to ground, protecting your devices from damage.

* Sags and brownouts are different. They are characterized by a reduction in voltage, not a sudden spike. Surge protectors are not equipped to handle these situations.

To protect against sags and brownouts, you would need a voltage regulator or a UPS (Uninterruptible Power Supply).

Here's a breakdown:

* Voltage regulators maintain a consistent output voltage, even when the input voltage fluctuates.

* UPS provide a backup power source, often using batteries, to keep your devices running during power outages or voltage fluctuations.

In summary:

* Surge protector: Protects against lightning strikes (high voltage spikes) but not sags and brownouts.

* Voltage regulator: Protects against sags and brownouts by maintaining a consistent output voltage.

* UPS: Provides backup power during power outages or voltage fluctuations.