I think lots of people would keep their (plain text markdown) notes in Drive instead of using yet another tool / app / service for that. Besides, having
unencrypted text files at your disposal (for... I don't know... peeking into?) would be an absolute win.
Besides the pure textual representation of such files (.md, .txt), you still have the same problem for any (natively) supported Docs file format. It is, somehow, in the user's own option to use Drive as a repo for ultra-sensitive info or avoid it (but, unfortunately, this informed opinion applies more often to the more tech-savvy people).