WPSSO Core Premium retrieves all product information from WooCommerce and provides that information to the WPSSO Schema JSON-LD Markup add-on (aka WPSSO JSON). When the WPSSO Shipping Delivery Time for WooCommerce add-on (aka WPSSO WCSDT) is also active, it instructs the WPSSO Core Premium plugin to provide information about shipping zones, methods, and classes as well. Using this information, the WPSSO JSON add-on includes a Schema shippingDetails property with OfferShippingDetails for each product offer.
If you prefer to exclude the Schema shippingDetails property from the product offers, you can add the following filter to your WordPress child theme functions.php file:
add_filter( 'wpsso_og_add_mt_shipping_offers', '__return_false' );