You entered into a contract with the seller to supply you with goods delivered to your address, and paid the seller.
Although I agree with this in principle, the assumption here is that the contract agreement includes guaranteed delivery to the purchasers door. I doubt that is stated anywhere and it becomes a problem because it is "assumed", and most likely not clear in the terms. The implied contract therefore is simply the sale an item and not the guarantee of any type of delivery service.
For every purchase I've ever made on ebay there were lots choices under delivery options including paying extra for insurance or tracking. Just because it wasn't offered directly, doesn't mean it couldn't have been selected or requested to mitigate the risk.
If the liability of an item remains with the seller until the receipt of the item is acknowledged from the purchaser then surely it would make sense that every ebay seller would include insurance or tracking in the item cost, to mitigate their own risk?
Surely also if the seller proves they have posted the item in good faith and as agreed they are no longer liable? Otherwise what's stopping people buying items on ebay, then claiming they never received it (when they did), then expecting a guaranteed refund from the seller? Sounds like a good scam and more people would be doing it if it was that easy! Just doesn't seem like a logical or fair process in my opinion.