I was under the impression that the code is for the lowest common denominator. Meaning, gcode reads the line and parses it, some printer hardware only have the capacity to run a few threads at a time and leave others open for constant use like sensors.

So it does only 2 axis at a time while printing. It could be a power draw situation too. running say, a hot end, extruder motor and the x, y, and z motors at the same time might not be allowed on certain boards, the fuse might blow.

I could be very very wrong on this, I've done limited research and assumed a few things. Because even playing around while writing gcode (just a few lines) I found that on my RAMPS 1.4 board that the code is executed in the way I figure it was parsed in order.

I could just be making a fool of myself by assuming a few things.

I'm happy to learn more if people know more and are willing to impart this information to the thread.

I do know my Delta printer moves in all 3 axis at the same time, so it is possible, but I feel that it's the way the gcode is being parsed by the particular firmware you are using.