The answer to 'why is my dimmer switch flickering lights' is that a flickering dimmer switch is often caused by an incompatibility between the dimmer and the type of light bulb being used. Dimmer switches work by reducing the voltage to the light bulb, but some bulb types are not designed to work well with dimmers and can cause flickering.
Common causes of dimmer switch flickering include using the wrong type of light bulb (such as an LED bulb not designed for dimmers), a faulty or old dimmer switch, loose wiring connections, or electrical interference. If the flickering is persistent, it's best to have an electrician inspect the dimmer and wiring to diagnose and resolve the issue.