Would it not be cheaper to put some 50 cals along the deck and man them?
Completely illegal. Only criminals can have guns.
Another problem is the train wreck of local and international laws regarding weapons on board. A lot of the shipping companies take the standard “we believe that armed crew members would only make the situation more dangerous” (where have we heard that before*) a lot of the companies feel that from a legal standpoint it is easier to deal with crew members killed by pirates than the ramifications of dealing with crew members making pirates dead.
*There are however valid concerns about gunfire and volatile cargo and fuel, munitions, etc on the vessel.
I had somebody tell we a few years back that there was a study on piracy and ship takeovers and found that when the pirates were met with small arms fire or crew served weapons during the attempted boarding or preparations for the boarding, the number of successful takeovers dwindled down to almost zero. (lol I think this report was “disappeared”)
Problems with Piracy:
Laws, laws and more laws. International and others, it’s just a mess.
What do to with detained pirates- more of a mess.
Hot pursuit, coastal navies and other issues.
THE DAMN RANSOM MONEY! Piracy is very lucrative and the sad fact is that a nitwit caught with weed will see more jail time than the majority of these jerks (for a variety of reasons).
Expense: Private security dudes are expensive (well worth it imo) and you still have the problems of local and other laws with these guys.
Foreign policy: Enough said.
Local complicity- Sometimes the pirates are actually members of local coast guard/riverine outfits and brown or blue water navies in the areas in question.
Bunch of other stuff I forgot to add into this mess of a post.