Welcome to the Google Docs Editors help community.
I've never really given it much thought to it because I don't share my devices with others, however I do agree that it is a bit of an oversight given that you may need to give your device to someone to help you with something (like typing something into a google search, or entering their contact details, etc) but that doesn't mean you also want that person to be able to open and access your files.
Google provides a feature to send feedback to the development/engineering team, and I encourage you to do so by following these steps:
In the mobile app:
Tap the ☰ 3-line icon in the top left of the Docs/Sheets app.
On the menu that drops down, go to Help & feedback > Send feedback
Enter the feedback suggestion, and add screenshot attachments.
Click the arrow send icon in the top right corner.
kind regards, Mr Shane PE volunteer (not a Google employee)