I've had Amazon ship a product from a given vendor once and then when I try to reorder the same product from same vendor, can't ship. One was a flannel lined table cloth! Nothing bulky, heavy, or anything shipping related that would be restricted, expensive, etc.
I know many online vendors only use say UPS or FedEx. Some have super high shipping since they only offer 2nd Day Air or other express type options. I know USPS is available and much cheaper, but some of those companies won't use USPS. Their choice and my choice no to pay the higher shipping and will go elsewhere, even if the item itself may be more expensive. I look at the total cost. I feel MUCH worse paying $25 + 25 shipping than I do say $40 + $10 shipping. It's like the overall "value" of the item is wasted on shipping, especially when I know the shipping cost could be much lower, but a company refused to go that option. Yeah, not really logical as the same end cost, but I refuse to give people business that over charge for shipping. Plenty of other companies to spend my money with.