All online systems suffer from this problem.
Bots are scraping websites daily, including places like archive.org, where they compile everything and save it for posterity. Half the time, your data is already saved by a third party, even if you delete it off a website.
Further, all databases have the option to flag something as "Deleted" and keep the original data while not showing the data on the main web page. Just because you "deleted" something online doesn't fucking mean anything at all materially. It just means they are hiding it from end-users. The data is very likely still there. This is why people who are bulk-deleting their comments on Reddit are shocked to find those comments later restored...... because they were never actually deleted to begin with. They were just flagged in the database as "deleted" and to not be shown to end-users.
Unless you are running your own server and your own service, you are at the mercy of strangers who are in full control over whatever data you share with them.
This has always been true, since the beginning of the internet.
This is why parents in the 90's told kids to not post personal stuff online.
Because once it is sitting on a hard drive on a server owned by someone else, it is not legally any longer your data, it is now the data of the person who owns/operates that server and the hard drive.
Sorry for this message being kind of aggressive, I am very tired of everyone just figuring this out for the first time and thinking somehow it only applies to the Fediverse.
It applies to every single service you sign up for on the internet. You're storing your data with someone else, and you don't control the server software, database software, or hardware. That data is no longer yours. You are effectively hanging out on someone else's property, and what you do on their property is being recorded.
This is not a Fediverse problem, this is an Internet problem.
EDIT: Forgot to add, it's also the problem that the Fediverse is trying to help solve by allowing individuals to run their own instances and thus be in greater control of what happens to their own data.