Because depending on the weight of what is being shipped, the $50/bag might still be cheaper than sending via overnight Fedex, DHL, etc. For example, I had to send a 22-lb package overnight via Fedex - cost was $67.68 total.

However, when I shipped Randy Petersen's 10th Anniverary gifts of FT via FedexGround (42lbs), it was only $17.44.

So if someone has the time to ship ground it's probably cost-efficient, but if it has to be there quickly then the airlines would probably be less expensive.

OVMV. Cheers.