Fair question Dax, and I'll ask you an honest question in return. Can you think of any single screen game that would actually coherently have 16 people on the same screen at the same time, since split screen obviously wouldn't work? In the case of Bomberman, I found the sweet spot was 6 players - but 8 was pushing it for actually being able to tell what was going on.
I'm genuinely curious - what would you do with 16 controllers on a console? Even with 8, I recognize that the times it might actually be used would be *incredibly* rare to the extent where it's at best a little "meh, kinda cool and I *might* use it one day, but I could do without" feature. 16 I could never see me using.
Edit: The potential for more than 4 people in a rhythm game is there as well. A *lot* of bands are five people, after all. Though, the logistics of this still put it as a "once in a blue moon" type of thing.