Why are the fees reset before calculating them?

Replies: 0

Within the cart class you have the calculate_fees() function.

/**
 * Calculate fees.
 */
public function calculate_fees() {
	<strong>// Reset fees before calculation
	$this->fee_total = 0;
	$this->fees      = array();</strong>

	// Fire an action where developers can add their fees
	do_action( 'woocommerce_cart_calculate_fees', $this );

	// If fees were added, total them and calculate tax
	if ( ! empty( $this->fees ) ) {
                        ....
                        ....

I was hoping to add fees to the cart using WC()->cart->add_fee() like you would do using WC()->cart->add_discount(), but because they are reset every time they are calculated, the only way is to use the hook.
Just trying to understand the logic.