Water is not very compressible; even at the bottom of the ocean a kilogram of plain water still takes up 0.982 liters of volume (compared to 1 liter at the surface).
However, actual ocean water is saline (salty), and the salinity of the ocean varies widely. Dissolved salt makes ocean water more dense than pure water; and the more salt there is, the denser it is. That's why it's easier to float in the ocean than in a freshwater lake.
Typically, the water at the bottom of the ocean is slightly less salty than the water at the surface. This is because evaporation happens at the surface.
The Them who wrote your American history textbook and glossed over the centrality of slavery to the Confederate cause, aren't the same Them who write TV sitcoms that propagate stereotypes of bumbling clueless men entitled to dump all the emotional labor on their hyper-competent women partners.
The Them who fund intrusive social media, aren't the same Them who dial down the yellow-light time on your traffic lights to catch more people with red-light cameras.
And the closer you look, the less it looks like a Them at all.
The individual TV writers were really trying to be good TV writers, in the social & economic context of TV studios.
The history textbook people were mostly actual professors. They want you to have a good history textbook. But the Texas Board of Education is giving them a hard time.
Heck, the social-media programmers mostly just wanna launch cool stuff.
The yellow-light people, though? They have no goddamn excuse.
Right now, this is a service being provided largely by volunteers, with some help from donors. For example, the lemmy.world instance is run by the same person as mastodon.world, who has posted some information here about the costs and donations involved in running Fediverse services.
As it turns out, it's not super expensive to run a public-facing Internet service with a few thousand users if you're interested in doing so as a hobby activity. And a lot of folks are willing to donate to help the project along!
More generally: Over the history of the Internet, new services have often been prototyped by researchers, students, and hobbyist volunteers. These folks are expecting to spend a little money to make the service work, and usually enjoy it when people using the thing they've built! They usually don't have an immediate need to monetize everything, but they often accept donations if you're enjoying their work and want to contribute that way.
The new domain owner — if they set up an ActivityPub server instance (e.g. a Lemmy) and got a list of the old user's post URLs — might be able to delete or edit the old user's posts stored on other instances. That is a vulnerability, albeit a small one.
If the old user was still listed as a moderator of communities hosted on other instances, the new domain owner might be able to take over that moderator role.
One way to fix this would be for instances to issue a public-key cryptographic identity to each user, and distribute users' public keys to other instances. Then activities purporting to be from that user would need to be signed by that user's private key.
Users' private keys would stay local to their home instance, so users don't have to do any key management themselves.
This would mean that if an instance goes away (and its key material is destroyed) then nobody can ever act as any of those users again. A new user created with the same username and domain would be a distinct user for all other instances too.