Aryl chlorides and bromides can be easily prepared by electrophilic substitution of arenes with chlorine and bromine respectively in the presence of Lewis acid catalysts. But why does the preparation of aryl iodides require the presence of an oxidizing agent?

(N/A) Iodination reactions are reversible in nature. The reaction is as follows:
$C_6H_6 + I_2 \rightleftharpoons C_6H_5I + HI$
To carry out the reaction in the forward direction,the $HI$ formed during the reaction must be removed. This is achieved by using an oxidizing agent such as $HIO_3$ (iodic acid),which oxidizes $HI$ back to $I_2$:
$5HI + HIO_3 \rightarrow 3I_2 + 3H_2O$
This prevents the reverse reaction and drives the equilibrium towards the formation of the aryl iodide.