Why do we do almost everything possible to haul out downed aircraft sitting on the Ocean floor, even something small like a trainer or a Cessna.
...but when a boat or ship goes down, we investigate it but usually just leave it.
Is it just for the black box, especially the flight data recorder?
Not completely.
I thought that was it at first, but when something goes down we grab debris, scrap, bodies

and often try to recreate it in a hanger - we collect pretty much anything that can be found. You probably already know they do this with commercial planes but private salvage companies do it too, for a cost. I know someone who is super rich because of it.
I ask because my Dad has owned a couple of big sportfish boats and he just got news that his last one sank off California. It came from New England. I have no idea how they got it there - way too big to ship on land as far as I know It was a 60 foot gorgeous thing with a huge back cockpit, tuna doors, tuna tower.
It had an EPIRB. I am pretty sure the EPIRB is just a signaling beacon though, and has no record of what systems failed. Kind of morbidly, many airplanes carry one too.
Anyway it sank in less than 100ft of water so it's totally accessible to an advanced diver on nitrox - and they're not going to pull it up, they're leaving it.
Any thoughts?