There are two situations where one party needs to rely on the other to get the best outcome for both parties - for sellers it's when an item arrives broken, for buyers it's when tracking says delivered but it hasn't been delivered to them - in the first case, as exemplified by this thread, the seller generally needs to reply on the buyer's willingness to assist with a claim, and if the history of this forum is anything to go by, that happens extremely rarely (poor data source, perhaps, sellers don't usually come here to "complain" about helpful and understanding buyers).

The second, the buyer can't open  / win an INR claim (they can open via PayPal, but wouldn't win) so they have to rely on the seller doing something about it (as a point of interest, if this forum is anything to go by - while still being a poor data source -  sellers opting to do absolutely nothing about it is extremely rare, based on the number of buyers who have complained about just such circumstances). 

Sellers have a little more incentive to take care of their trading partners, I suppose, but these are the risks of buying / selling online. Knowing buyers have little to no incentive to make any effort to ensure their trading partner doesn't suffer a loss and will rarely, if ever, take an inconvenient action that's not out of self-interest is just one of the things sellers have to accept - one of those "cost of doing business" things. (Side-note, I'm not actually sure I would ask a buyer to do this TBH, I mean aside from the "why should I have to do anything?" response that I'd expect, I have self-insured for losses like this anyway, it just keeps my life simpler and a little more stress free, when I add extra cover, it's purely for the loss cover, if the package goes MIA). 

I'm not really sure why everyone is assuming the package was inadequately packed, I certainly am not privy to that info, it's possible, but it's also possible the package was mishandled to an extreme degree - ever seen a delivery driver throw a package over a fence? A package been run over by the delivery van? These things (and more) happen, and would often break contents no matter how well they were packed, and 100% the liability of AP.