You're correct; the focal point revolves around data ownership. However, you have to ask yourself, do we actually own the data?
Currently, four major hosting companies dominate the fediversum. Instance owners in practice do not have full control over the physical servers where their data is hosted.
Do you own the disks on which the data is hosted? No! The hosting companies retain that ownership and, can wipe the contents with a mere click.
A regular court order is all it takes, and I question whether every instance is backed up? While some may indeed have backups, they might reside on the very same server. Others, although having backups, may execute the process improperly. Additionally, there are those with partial backups, and the list goes on.