It appears somewhere in all the recent changes, eBay may have missed mapping some categories that should qualify to use USPS Media Mail as a shipping method.

Sellers have been dismayed to find items they correctly sold with USPS Media Mail as the shipping option are not able to have a Media Mail label printed through eBay - the option is simply grayed out and the only other options presented to purchase shipping from eBay are more expensive methods like priority mail.

Shipping Media Mail
Ebay is not allowing me to print shipping labels for media mail. I have been selling Sheet Music and books since 2006 and have not had this issue before. Ebay message when I try to print labels is my items are “not eligible to ship media mail” but per USPS sheet music/printed music qualifies as medi…
MEDIA MAIL OUT THE WINDOW???
EBAY SUDDENLY EXCLUDED MEDIA MAIL ON MY STORE, WHICH I SELL MOSTLY MEDIA ITEMS! I’VE CALLED THEM TWICE, EMAILED ONCE, AND CHATTED JUST NOW. EACH AGENT CLAIMS IT’S AN I.T. PROBLEM AND THEY HAVE NO IDEA WHEN IT WILL BE RESOLVED. IN THE MEANTIME I HAVE CUSTOMERS WAITING FOR THEIR PRODUCTS!!! ANYONE …
Unable to Ship a book under USPS Media Mail - Item 194022573008
Hello, The system is not allowing me to change the shipping method from USP to USPS Media Mail to item 194022573008. I need assistance. Thank you
Shipping Dungeons and Dragons Books via Media Mail - Now Not Allowed When Purchasing Shipping???
I’ve been shipping D&D manual, instruction books, and modules via Media Mail for years and have never had an issue with purchasing shipping through eBay. However, on my last two sales, I’ve gotten the alert when trying to buy shipping through eBay that my sale category doesn’t allow MM shipping. I…
Media Mail grayed out
We have sold music books for the last 10 years shipping almost exclusively using Media Mail. Now starting earlier this week Ebay will not let us choose Media mail as an option when shipping. It is grayed out. Is anyone else had this problem?
MEDIA MAIL NOT WORKING
I have sold a book, but eBay will not let me use Media Mail. I have to send either First Class or Priority.
Shipping
I sold a CD on Ebay. I listed it as music with Media Mail for shipping. I have sold many CD’s this way. When I tried to use Ebay Shipping to print the label, it states the BUYER paid for Media Mail but I do not have the option to use this method. It is greyed out. My only option is First class or mo…

eBay community staff acknowledged the issue on July 14th and said

There is a known issue that is causing Media Mail to be grayed out in some valid categories. We're working to resolve this. Thanks!

There has been no further update from eBay on this issue.  For now, affected sellers with items that do qualify for Media Mail will need to purchase shipping labels through PayPal, a third party postage service like PirateShip, or directly from their local Post Office.