Good question. Maybe I'm unclear on the definition of "driver." I've used the term to describe the code that exercises the functions of the chip but provides human readable function headers. It's usually not ridiculously hard, interpreting things like register bit definitions and timing diagrams. And in the absence of published code, I'd have been on the hook to write it myself anyway. Often, talking to something like an ADC through a SPI port on a microcontroller might be 10 or 20 lines of code.