Is there a technical motivation for doing that (low-latency, reduce
bandwidth to allow staggering multiple LPs on a single MIDI bus, etc) or
was the protocol simply designed by the marketing dept?
I think it was driven by cost reduction mainly. It was pretty much all they could manage with the low cost MCU they used.
You can see all the details in this teardown. Look at the comments too for some insights from one of Novation's engineers.