They changed how variations were displayed by default in WooCo 2.4:https://woocommerce.wordpress.com/2015/07/13/improving-the-variations-interface-in-2-4/
function soflyy_change_threshold( $amount, $product ) {
return 100; // change this to the amount of variations you want to load
}
add_filter( 'woocommerce_ajax_variation_threshold', 'soflyy_change_threshold', 10, 2 );