Media rate (Books/CDs/DVDs/Games) all have the restriction. The only one in the category is the varied weight of books. The others are all known how much they weigh and the associated cost to ship.
With regards to the Wild West days of charging excessive shipping on low bids, eBay used to not charge a fee on the shipping. So a seller could sell an item for a few bucks while charging an excessive shipping rate in order to circumvent the fees while still yielding an acceptable total for the item. Now, the eBay fees are based on the Final Value which includes shipping.
So there are different approaches in compensating for the loss. One is for the seller to charge a handling fee on top of the shipping fee such that the cost of shipping/materials will not incur a loss for a seller because eBay still charges the fee on handling and shipping. Two is to not bother with the calculus of handling and charge just the calculated rate with the hope that the minor discount on shipping labels offsets eBay's take and your costs. Three is to offer free shipping so as buyers are unable to leave feedback on shipping details and the idea that buyers might bid more if they don't have to pay shipping.
I'm not sure the third choice can be proven consistently where the seller is not losing money beyond the cost of shipping but in incidental costs associated with shipping. The one benefit is that buyers can't leave feedback on shipping details. Some buyers just hate shipping costs and have an unrealistic idea of what the actual shipping costs are. Shipping is expensive and is never "free". I'm a power seller for nearly 20 years and always charge a calculated shipping cost. I don't pad the weight of an item or charge a handling fee to increase the costs to the buyer. Yet, when you look at my feedback (still 100% positive overall), the specific feedback details indicates that some buyers have left less than 5 stars on the shipping charge. Somehow the buyers think I'm responsible for passing along the same costs that I incur as being excessive.
I'm an Impatient Buyer.
Most Sellers Respond within Minutes of My Buying.
Most sellers Supply a Tracking Number same Day, If I Buy in the Morning.
Used to be Both seller & USPS would be on the ball, & next Morning I would be tracking,and Have my Package within 3 Days.
It spoiled Me.
Now USPS Either Ships the wrong direction then Turns around and Slowly Ships Back with the words it's "Moving within the system"
like they don't have the slightest opinion where it is and a week or so later, say it's out for delivery.
Now I see they are Charging for Full Tracking
They also ship Thousands of Packages for Free from China, Etc.
and UPS & FED EX occasionally transfer packages to USPS For Delivery .
USPS Does NOT deserve a Raise to pass on to the General Public to pay !
But any way, My original Point,

When I Get my Package a week Late, I'm sitting here Thinking giving the Seller Bad Feedback,
once it arives I Calm down & Figure Why give bad feedback to the Seller ? I Wish the Bad feedback would go to USPS !
My coffee Delivery is the Same way.
Used to take 48 Hours From Philly to Central PA.
3 transfers (Factory to Philly, to Lancaster To out for delivery)
Now from Philly to Maryland, Disappears for 3 Days,"Moving within the System) Shows up in Lancaster, Shows up in Lancaster again,leaves Lancaster, Leaves Lancaster again
& 24 hours to 48 Hours later it's out for Delivery

(btw Lancaster is about 40 Mile) they must be walking and handing it off to Mailmen Like runners Hand off a Stick during Races.
But in Slow Mo