Developing USB drivers is actually totally fantastically easy nowadays with libusb(x). You can more-or-less just pretend your USB device is a server you talk to through a socket. No need to even write a single line of kernel-code, you can do it all in python in userland, if you so desire.

For many USB devices this is also a totally feasible thing to do, too, because most USB devices that are not providing some standard interface that the operating system takes care of (keyboard, mice, controllers, tablets, mass-storage, ...) just provide some sort of service that typically only one application would interact with, so just having the driver inside that application that interacts with it works well.