Google is the most targeted company by hackers for sure. Google sit on exabytes of personal data, and it's like hoarding tonnes of dangerous radioactive waste, which if it got in the wrong hands, could be very dangerous. That's why their security is unparalleled. They have a lot of dirt on people.
Big companies' data collection is on the whole quite subtle, and they like it that way. Google will suck up tons of data, digest it, and use it to throw ads at you. But it doesn't really occur to anybody that Google might be interested in looking for people picking their nose in front of their phone's camera, and making a compilation of that to present as "art". If anything of the sort happened, Google would make sure to make an example of whatever rogue employee did that. They like their data collection to be obscure and harmless looking. That's not to say that it is harmless, but finding problems with what Google is doing takes at least a bit of intellectual thought.
Meanwhile, an artist secretly recording people is almost certain to have some sort of quirky agenda that's going to immediately turn a large amount of people off, even if it's ultimately silly and non-consequential.
Can you explain this one?
In general, I mean that having your picture taken at the wrong time can reveal things people would rather not be revealed, even if to the photographer it looks completely ordinary and harmless.
Some people here will reference the 24/7 CCTV surveillance, but that's kept private and not published as some sort of art project. So though one could compile a video of my coming and going around the town by looking at surveillance tapes, in practice that doesn't really happen. Now random photographers and artists however are very likely to put their work somewhere public.
A normal picture of a person could still expose something important about them to the wrong party. Eg, "I visit the unsavory part of town", "I'm not really washing my hair", "I'm slacking off", etc. Those are mostly "real-world" concerns.
There's the paranoia angle: some stranger wants your picture specifically. What could they have in mind?
If you look at least somewhat remarkable, you might end up being part of some meme, or being photoshopped into something. You might be the next Magikarp Guy, if somebody snaps a picture at exactly the wrong moment.
With Google the concerns are quite different. While Google pries a lot, so far it's mostly invisible. Google fortunately isn't run by edgy teens looking for the maximum lulz, but by boring accountants looking for profit. So though there's still plenty things to be concerned about, the concern isn't as visceral.