Even beyond that, USB is available on many microcontrollers, a USB CDC device is dead simple to implement, the drivers are baked into every modern OS, and all t

Even beyond that, USB is available on many microcontrollers, a USB CDC device is dead simple to implement, the drivers are baked into every modern OS, and all the software developers operating at that layer already know how to interact with text streams. Add in the ease of debugging when you can just manually send/receive ASCII to operate a device, and you've got the makings of a standard practice.