At some point, the owners of these vessels are remiss in ignoring the safety issues of the crew members.
>>>>> I just can’t buy that. <<<<<<
It’s not a question of you “buying it”.
The entire concept of territorial waters and international waters (”the high seas”) is that each sovereign nation have sole dominion over its local waters.
Hence the laws and customs of each country apply to 12 miles from each country’s coastline.
And those laws and customs can often include prohibitive firearms laws.
Under those conditions, commercial shippers (and recreational sailors) are not going to risk the seizure of their vessel by allowing firearms on board. They never know which countries, localities, and ports do or do not allow firearms to be transported on the ship.
So until each and every country’s firearms laws are changed in each and every local shipping port around the globe, sailors will be cautious about having weapons on board.
Or by international treaty, but that’s also unlikely.