@tombie
I've been in this situation several times - last time was just today.
Some people us the fact that they don't know if there were chest on board as an explanation/excuse (hard to judge which one fits for every single case).
The way i see it, it's still pointless to use up your supplies to drown a ship and jump to the sharks to hopefully get a treasure.
If someone looks for treasures on those ship, just park your ship near and climb on the targeted ship - it's way saver.
Other players have another explanation, which i think they are honest about:
They just want to kill everyone - probably because they feel stronger if they sink an unmanned ship or something like that? Or they think this is a way to portect themselves?
Either way: yes, pvp is always on, to create savezones would actually disrupt the open world/sandbox feeling, i guess.
I don't like being attacked while restocking or being hunted across the map by bigger crews too, but what should we expect from the community?
Let's hope those kids (just my assumption who this could be) get bored quite fast, so the ship encouters will become more of an honorable fight instead of a stab in the back.