They are not. Not only is it a profit centre for them, but it allows them to stop the practice of making a low asking price then attaching a huge shipping price. (For example, a poster recently was told that his $5 item will cost $125 to ship from the USA) (This is actually not covered by the policy, but that was the sort of thing that was happening a LOT).
Some things are not practical for mail order. Low priced but heavy or bulky items are among those. I take it you are complaining about the romance novels that sold for $6.50 not the similar larger lots that sold for about $25. Once you start looking at the dimensional costs of shipping, you will easily see how many books you can put in a lot before the rate goes up.