You are very late to the ' Combined Postage' party!
This issue has been going on for a very, very long time.
eBay we are told, are aware and ' working on the issue' till now, now fix date anywhere near, to be announced!
Some sellers are leaving a message on their listing, for example..... ' If you wish to buy multiple items, please let me know before buying, I will relist them as one listing so only one postage cost is charged, combining postage is not currently possible. '
@sweetcuppi