I've been victim to many betrayals throughout my time playing Sea of Thieves, most of them happening with alliance members at skull forts.
They often sink my ship and kill me (and any crew mates I may have), and take the loot to an outpost.
This time was super weird however. So weird that it was literally pointless for them to do, because it wasted both our time and possibly lost them their ship with all its resources. What happened was, me (playing solo on a closed crew, after getting tires of countless random noobs) and another sloop joined alliance after they showed up at the fort as I was dealing with it. When we killed the boss the other guys opened the door and started taking everything out. No one blew up a gunpowder barrel or anything.
We placed EVERYTHING on their ship. They sail away while I'm going through the fort looking for any lose gunpowder barrels and resources I could collect. When I get back to my ship I see it swimming away full speed. I take the mermaid and find it empty, so I drop anchor.
While re-positioning to head where they were going, I notice they tried blowing it up with the barrels I had. They dropped most of them from the crow's nest, onto the mast and one on the deck. I think the guy accidentally fell off the ship and didn't get to shoot the barrels.
When swimming away the guy (or his friend) left the alliance, meaning I would get [Mod edited] from all that loot. So since I wasn't going to get anything, I thought I might as well get some payback. I went to Plunder Outpost where they went. I see their ship docked, sails up. I drop anchor next to it, grab a gunpowder barrel and blow it up on their ship.
One of them returned at that point and started shooting at me, so the next barrel I just put under the ship, underwater. It unfortunately killed me, and when I respawned they have already filled the ship below deck with my barrels, I tried taking the closest one and running out of the ship with it, but someone managed to shoot me and they all blew up. By the time I respawned I was already far away on a new island with a new ship.
Here's the reason why this betrayal was absolutely pointless for those of you who aren't as experienced. When you're in an alliance, you get 100% gold for whatever you sell, and whoever is in an alliance gets 50% on top of that. So there's no split in profit. They would've still gotten the full 100% if they didn't betray me, and I would've gotten 50% on top of their profits.
If anyone here is well educated in psychology, could you please explain to me what is wrong with their brains, or what was going through their heads to do this?