If people couldn’t be unethical at scale then Facebook wouldn’t exist at all and yet it does, so I’m sure the same would be possible at Google.

That's different. People can easily be unethical at scale when incentives align. What they almost never can be is coordinated at scale against the individual incentives - whether for good or bad.

Also maintaining that deleted data is an issue, can't just magically move it to your datacenter in the mountains. someone will notice the movement of data even if it's automated. i suspect google just extracts as much data as possible from the photo, maybe trains an algo or two with the metadata and then deletes