No country is going to let an armed ship enter it's waters.Besides, last thing you want is a gunfire on a ship, and on a tanker, it would result in a catastrophe, no matter how trained the security forces are.
Interesting quote:
A spokesman for the International Maritime Bureau said that, while shipowners had the right to take such measures, the organisation advises against them doing so, for two specific reasons.
“Number one, if you do start carrying armed people on board, the tendency of the other person to pull a gun and use it with the intent to harm is going to increase if they find out that you have an intent to harm them. That could result in loss of lives,” he said.
“Secondly, if you are on a chemical or gas tanker the last thing you want is a firefight between pirates and security people on board.”
For now, the only and best option would be to increase patrols in the critical area, and keep the pirates in a distance from Civ.Ships.
Also, a lot of ships do not take all the necessary security precautions and do not stay on a safest , guarded route.
My father is a captain on a world class freighter, he passes through that area very often so it's not very "all the same" to me.