Shadow IT. A client asks: if we cancel our subscription tomorrow and our competitor acquires your company next year, will our data have been deleted by then ? And if you have employees sharing customer data with each other over unsanctioned channels, you can't really answer "yes".
Blocking Google Docs is by far the cheapest way to prevent its use, even considering the downsides of a complete block.
I'd recommend suggesting that they whitelist /preview as that is a view only mode that allows you to access external docs without leaking data to the world.
Does that mean they block every single website where you can upload data? Dropbox, Gmail, etc? What's even the point given how easy it would be to find some way to send stuff over the Internet?
Yes. It's trivial to block everything you can think of easily, and for everything other than that there's network monitoring and legal recourse.
Why would you bother to look for some awkward way to work with customer's sensitive data over the internet, if you're going to get fired for finding that way? The main goal is to prevent random people from storing data in unapproved locations "because it was easier that way". You can easily make it not be easier, that cuts 95% of the sharing, and then the only practical reasons to do so are clearly malicious.
Assuming it's not a troll question: banks and insurance companies store sensitive financial information about customers. So they dont want any of their employees to use dropbox or the like
