Do you understand that of you for to the calculator and ask for a price it uses YOUR ZIP code as the "delivery address"? Obviously someone across the country is going to pay more as the distance increases.
On the couple of seemingly larger items you have lusted you only offer "expedited shipping" followed by "Priority Mail". FedEx was not even an option.
So basically, to your question "why does this keep happening" the answer is you have your listings set up completely wrong.
"Laissez-faire capitalism (AKA The Great Material Continuum) is the only social system based on the recognition of individual rights and, therefore, the only system that bans force from social relationships." ~ Ayn Rand
