Exactly, their hands are tied by Ebay/Paypal rules, if they want to remain protect from false claims by buyers, or lost packages in the mail.
But I can imagine it might be a future requirement on ebay, if ebay/paypal gets tired of having to resolve disputes that could have been avoided if trackable shipping was used. Until then, for small/cheap items, find and use sellers who don't protect themselves with the more expensive tracking options.