I disagree, for exactly the same reason . USB is a PITA and unnecessary overhead for adding simple hardware to a device.
Strapping a computer to the back of my computer so I can add a simple sensor takes space, costs in components, and most importantly takes time messing about with unnecessary (and usually poorly documented) code. I hold my hands up here as a simple minded hardware designer, I hate writing code and do it only where needed.

USB in addition to i2c (or SPI, or even rs232@3v3 if you wish) by all means, but not to the exclusion of a simple interface please!

I think there were limited TOH produced because the software and documentation never encouraged experimentation without spending a lot of time digging around looking for information.

It took me days of searching just to figure out how to get a GPS fix in a python script when the Jolla screen is off FFS!