[user5994461]

>>> Honest question: what is so complicated about writing device drivers, whose sole purpose typically is to transport data from input to output, and vice versa?

Transporting billions of data per second from multiple inputs and to multiple outputs, on the fly in real time, within the processing and performance limits of all the different pieces of hardware involved, on a shared system.

>>> Also, shouldn't drivers be sandboxed to prevent stability problems from affecting the rest of the system?

You cannot sandbox a driver, the driver sandboxes you.

If it helps you, think of the drivers as a sandbox are your app. It sandboxes your app access to display, hard disk, keyboard...