> Google can't do that. Even if they work at Google they can't get it.
I'm not sure I understand this point, so let me make my point clearer. It's clear that Google(TM) can access your data. You probably mean "most google employees can't", which I agree with. But someone can access your data for sure, and in fact you can access your data: if you are a European citizen, you can request all of your data right now, thanks to the GDPR and Google has to comply. There are also other general tools to access the data[1].
So I'm not saying "a Google employee will go behind your back". I'm saying that either "Google(TM) could be compelled by a court order to give your data if laws change", or "someone could use your unlocked PC, click on 'Download my data', and give it to the other part" (again, more likely if the other part is tech savvy and planning on divorcing you).
> I'd like to hear if this has actually happened to anyone anywhere.
Someone getting in trouble because someone took their private information? It happens quite often in the Legal Advice subreddit. Here's one example[2]:
> "My wife uploaded screenshots from my Ashley Madison account, hotel receipts and non-nude but sexual photos of me online before she moved out and filed for divorce. Do I have any legal recourse under Delaware law? (...) They were not public. The photos were from my phone and were not anywhere online and the credit card was in my name only. She had no right to access either one (nor my Ashley Madison account)."
My specific case? No idea. But supposedly private information biting someone back is a regular event. Here's a page some lawyers in Orange County wrote on that [3] with some examples.
* Edit: rethinking my point, I think you meant "how is this a Google problem, rather than an infosec problem". To that, my point would be: the fact that the information exists forever in one central place.
[1] https://medium.com/productivity-in-the-cloud/6-links-that-wi...
[2] https://www.reddit.com/r/legaladvice/comments/5b895c/my_wife...
[3] http://orangecountydivorce.com/divorce-technology/