OP - As a buyer, I totally understand your frustration.
But Feedback is, and always was, voluntary. Where is it stated that sellers must leave feedback first?
Are you buying an item or feedback?
As a seller, I don't leave it first anymore. The transaction is far from over just because the buyer paid "fast". If a buyer emails me and says "I received the item and it's great, blah, blah, blah, then yes, I will leave them feedback first.
Due to ebay and their ever ongoing rules, we sellers are not able to leave honest feedback anymore, so some sellers have given up on it.