I've never asked google search to write my emails, presentations, or feature proposals. Nor to summarize company documents like reports, memos and the like.
Been a while since I was at Apple. But we never used Google services and any third party tools we did use were vetted by a cross functional team from Security, Data Governance etc.
This idea that they would just allow sensitive data to be given to competitors in an unmanaged way is ridiculous. That sort of thing doesn't happen at any enterprise company let alone one of the most secretive in the industry.
For policy setting that's the wrong question. The real ones are: how likely is it to happen, how much would training/comms change that, and how acceptable is that risk. Their answers seem to have been: very, not enough, it's not.
Where the problem is and how to change it is an interesting topic, but likely irrelevant for the decision.
More than a decade ago when i worked in software security google was banned from work stations. Both due to it spreading virii via ads and also due to tracking.
Fast forward to 2018 at a large corp for critical code and data chrome was also banned. Regular workers not but certain webapp features had to be sealed off.
Do they realize it's the same info being tracked?