When selling why does payment received not include postage,only item sale price?

When an item sells and is paid for the payment received column only shows the items selling price and does not include postage

charges even though the buyer has paid it. I just think it a little strange that if for example I am paid $19.40 via paypal but payment received reads $9.50. I have looked through the ebay answers but could not find any answer. Maybe I missed it.