Delivering batches of household goods of arbitrary size profitably is a hard problem that no one has figured out. Everyone is fiddling with business models trying to make it work.
I think at the end of the day shipping is expensive and trying to hide that from customers without incentivizing profit-negative transactions is nigh impossible.
Things will probably change when we have droids roaming the sidewalks, but until then these strange charges are going to keep popping up.
Wait, wait, I think I've figured it out. Raise the price. Repeat until either the transaction is sufficiently profitable, or the customers go away.
That will work better for everyone than what Amazon has started to do lately, which is prevent you from buying certain items at any price until your order exceeds $25.
Basically, Amazon has started to tell their customers "No." That's new, and I agree with the other posters who call it a bearish sign.