To be fair, part of this is probably because of their desire to save the buyer money. These fish probably needed a much bigger box, bigger bags, more water = more weight, more girth, more money to ship.
The shipping alone should probably have been $20 or perhaps more, and with each fish between...oh, I don't know...$5-7, they would have had a hard time selling what are probably somewhat common fish in metro areas.
They could've shipped flat rate medium or large box if that was the issue. With regular poly bagging water is not as important as o2 volume.
I can only speculate on why a large fish in a small breather bag fails, but my best guess is that there isn't enough water volume for that size fish, and either the water quality deteriorated rapidly due to toxins in the water, or just the lack of the breather bag exchanging gases fast enough.