Or, perhaps more directly, training their image-gen models on your private Google Photos.
They’re training (with an opt out) on stuff people feel is an invasion of their privacy to make their service better.
And this is the problem: any time you're adding a new "feature" that invades users' privacy, it needs to be opt-in.
And again: Google did this and everyone eventually got over it. Cars do this with telematics data and everyone is over that too.
The only reason that worked is because Google is an unstoppable monopoly juggernaut whose name is literally synonymous with searching the web.