They don't delete your content, they just redact your username and disassociate each individual comment from your larger profile so nobody could, for example, click on the deleted user who posted a comment in r/abc and see they also posted a particular comment in r/xyz.

The reason tools like Redact (many of them all use this same name lol) have taken off in popularity is because they delete, or redact the contents of your posts before you delete the account, thus making even that vestigial data worthless.