Because if you pick on navy vessels, you get owned.
Pirates caught redhanded by one of Her Majesty’s warships after trying to hijack a cargo ship off Somalia made the grave mistake of opening fire on two Royal Navy assault craft packed with commandos armed with machineguns and SA80 rifles.
In the ensuing gunfight, two Somali pirates in a Yemeni-registered fishing dhow were killed, and a third pirate, believed to be a Yemeni, suffered injuries and subsequently died. It was the first time the Royal Navy had been engaged in a fatal shoot-out on the high seas in living memory.
By the time the Royal Marines boarded the pirates’ vessel, the enemy had lost the will to fight and surrendered quietly. The Royal Navy described the boarding as “compliant”.
I'm not criminal mastermind but if you're floating around in a stolen fishing dingey, you might want to give it up when commandos show up. Just a thought.