I'm surprised that many posters here are surprised.
This has been the case for years. The big couriers even stated why several years ago - poorly packed instruments leading to massively increased claims. Shops negotiate their own deals, or use their business insurance to cover any courier based losses. Shops are also less likely to put in a dodgy claim when compared to an ebay deal.
There are couriers out there who will insure properly but most of them require a phone call and not just a web form.
IIRC ParcelFlight are used by Bass Gear for Foderas and the like, and I think UPS will do full insurance if you get a bespoke quite over the telephone.
And for those complaining about them taking the money and then you discovering this.... you know that little "I HAVE READ THE TERMS AND CONDITIONS AND AGREE THEM" tick box that you had to tick before the payment was taken.... the details were all in there. You just didn't read it. That is not their fault.