So where is MEGA2560.h or what ever they call it located?
Habit I guess. Multiple protocols? Just write a function as required. Like I do for the serial ports. When I started with 8051s there were no I/O functions pre written. You had a standard K&R C compiler with a relocator for the specific processor and that was it. When I had to use VGA chips, you programmed the registers one by one as needed.