The answer to 'why is my dimmer switch hot to touch' is that a dimmer switch can get hot due to the electrical resistance and power dissipation involved in reducing the voltage to the light bulb. This is a normal and expected behavior, as dimmers work by limiting the amount of power going to the bulb.
However, if the dimmer switch is getting excessively hot to the touch, it could indicate an underlying issue. Some common causes include an overloaded dimmer, a faulty or damaged dimmer, or an incompatibility between the dimmer and the light bulb. In these cases, it's best to have a licensed electrician inspect and repair the issue to prevent potential fire hazards.