Because it's really important for publishers that users can't edit their saves on their single-player-but-always-online-with-insane-amounts-of-grind-and-ingame-microtransactions. Think about the profits!
At the other extreme I love what Stardew Vally does here; saves are cross-platform and in a simple XML format. You can edit it and people even make things like https://upload.farm/ to share games and ideas.
I don't think it'd be a fool-proof mitigation but something I believe would move beyond a single point of failure (which, evidently, savegames alone are) is to hash the saves. You can then upload saves that match either one of your own hashes.
Hopefully, the system would be architectured so that even if the saves themselves went missing the table of hashes is still around.
Yes, indeed, it would be problematic if they lost the hashes as well. I'm just imagining that it'd be easier to ensure there is redundancy on something like hashes which would not require as much storage to duplicate.
