A way to assure Sunken Chests from messages

[ADM]

I'm playing on a world on which I currently counted 13 Message in a Bottle opened without getting a treasure, and this is only since I started to count, I haven't got a single Sunken Chest yet (day 300~) and made sure that they could spawn in theory (not caused by mods) in a backup save and they can (so not a bug either), and that there is in fact not a single underwater salvageable in the world with commands.
For some reason, I'm absolutely out of luck this time and this is annoying me my friends a ton.

 

There is a thing I might have suggested in the past, can't recall, but that I still look forward it to be added :

Returning the Cracked Pearl to the Crabby Hermit assures messages to be treasure hunts.

As simple as that. Returning it has no much benefits, it's a honest gesture but frankly... that could serve something as well.
and, uh, not exactly a Crab King loot buff but are you guys still not gonna improve them ?