I'm not going to do the research for you guys, but do Wii U Fit or Wii U Sports that can be played multiplayer locally have online multiplayer? What about multiplayer fighting games like the recent Mortal Kombat and Street Fighter? Or to take it even closer to home, Amplitude 2?
If you want to say that Rock Band 4 should have online multiplayer because it's designed for local multiplayer, that's just the same as saying Fallout 4 should have had online multiplayer. The game's system lends itself well to a sort of MMORPG kind of thing.
I don't know about the Wii games, but both Mortal Kombat X and Street Fighter V have online multiplayer. Neither of which really work well (or at least that beta for STV didn't), but at least they tried. Also no, this isn't like saying Fallout 4 should have multiplayer, because that game is built for single player play. Whereas Rock Band 4 out of the box has multiplayer, it's just local and not online.