Why is the main reason to move the person in need of to a dry area when using an aed?

Because it avoids the risk of electric shock.

Explanation:

AED is the acronym used to refer to an automated external defibrillator, which is equipment that allows the application of an electric current to a patient's heart. And it aims to prevent your death from cardiac arrest. The External Automated Defibrillator (AED), a device used in this procedure, is also indicated to treat arrhythmias, atrial or ventricular fibrillation and tachycardia.

As the AED works by applying a lightning strike, it is important that the victim is transported to a dry place (and has a dry body) before the AED is used. This is because, as water is a conductor of electricity, its presence in the use of AED may increase the risk of electric shock to the victim and the rescuer.