I don't get why that should be the case. When you rent an apartment the owner is generally no longer able to just walk in and do whatever he likes, including installing cameras in the shower. So I would expect that when Google tries to sign you up for its online storage (repeatedly) you should get the same protections, especially with smart phones being such an important part of modern life.
From one perspective, I understand that cloud storage should include certain rights to privacy. If I buy some compute time on AWS, I manage and control all flow of data. It would be a complete violation if AWS policed the kind of content I could store. I think self-managed vs company managed is what dictates my expectations. Google photos and drive, especially since most people don't pay for it, fall into the company managed category in my opinion.
In the last few years Google Drive became more strict about sharing copyright work and started flagging files, which limits the ability the "share to anyone with a link". For people who use it as a backup, the advice I started hearing was to encrypt the data before uploading. The opsec while considering nation-state level threats to privacy already recommended only using encrypted containers since the beginnings of cloud storage.
The Communications Decency Act is an interesting law that dictates the liability of online content and service providers. There is an ongoing battle to increase ISP and host liability as a way for the entertainment industry to combat piracy.
FOSTA-SESTA and the ruling on Backpage [1] made things more difficult for hosts like Google and changed the liability surrounding sexual solicitation. If a host like Google knows what's being hosted and does nothing, they get in trouble. They don't have the protections they did in the past.
Just to give context to perspectives people might have on this analogy, the above would be illegal in e.g. Germany.
Again, the parents Google is reporting to the police are not trying to share photos with anyone except their own doctor.
This isn't scanning information because you made it publicly available. This is scanning information on your device because it was automatically backed up by Android.