How is it unbelievable considering that these devices are so much less efficient in terms of h/w? Why would someone spend their time and effort writing code for the hardware that no one in their right mind is gonna use for mining on any significant scale?

Combining any number of ARM devices into a cluster doesn't change anything in terms of their efficiency. It's just you either have one device that sucks or you have a bunch of those working (and sucking) together. That "FREE and GREEN" energy could be used to power more efficient GPU rigs, and instead you want to waste it on your ARMs.