Show all options on the first select for a WooCommerce variable products even if not available

woocommerce_variation_has_changed.js

(function($) {

	$( '.variations_form' ).on( 'woocommerce_variation_has_changed', function( ev ) {
		$( this ).find( '.variations select' ).each( function( index, el ) {
			//Get the first select current value
			var value = $( el ).val();
			//Get the original HTML from .data( 'attribute_html' ) and replace it again on the element. 
			$( el ).html( $( el ).data( 'attribute_html' ) );
			//Then set the value again
			$( el ).val( value );
			return false; //Only the first one
		});
	} );

})( jQuery );