I agree in principle that a privately run company could use information in nefarious ways internally, and that barring any additional knowledge you should not trust them.
That being said, I have an anecdote as a former googler: the reality with Google though is very thoughtful and favorable for users if you ask Googlers who've worked on their software products. There are audit trails that can result in instant termination if it's determined that you accessed data without proper business justification. I've known an engineer who was fired for an insufficiently justified user lookup (and later re-hired when they did a deeper look -- hilariously they made this person go through orientation again).
And safeguards / approvals required to access data, so it's not just any joe shmoe who can access the data. Wanna use some data from another Google product for your Google product? You're SOL in most cases. Even accessing training data sourced from youtube videos was so difficult that people grumbled "if I were outside of Google at OpenAI or something I'd have an easier time getting hold of youtube videos -- I'd just scrape them."
This isn't to say any of this is a fair thing to make decisions on for most people, because companies change and welp how do you actually know they're doing the right thing? Imo stronger industry-wide regulations would actually help Google because they already built so much infra to support this stuff, and forcing everyone else to spend energy getting on their level would be a competitive advantage.