Quicker .... less exposure to salt .... the booking agent made a good deal .... the airlines needed the money.
I'm thinking that at about 12 or 14 pounds a kit it would make about 275 kits (thinking small arms, not heavy guns) with packaging. Probably not enough to merit shipping by boat, and maybe about the same overall cost. And much faster than waiting for a container of small shipments to the same destination to get filled and shipped by boat.
I could be completely wrong, of course. But it would seem unwise to ship several hundred active machine guns in one single shipment if you were a small terrorist organization. A number of smaller shipments would seem to have a higher probability of success in getting some through. Of course, this could also be a smaller shipment in a much larger operation.