I don’t know if you’ve participated in a large group chat, but on those occasions, lots of media is being sent to each other.

I am not that eager to have every media sent in the group chat stored on my Photos library. I don’t think anyone wants that.

So I guess everyone, including me turns off that feature (automatically storing images received), meaning no one will eventually have that image stored on the device which causes the data loss after a while.

Now, there is a backup feature in iOS, but it can only backup to iCloud drive, which I don’t pay for so the limit will be exceeded pretty quickly.

I wouldn’t put the blame on anyone for this, except Whatsapp.