Rock Band 4 not coming to Wii U because "the audience is not there"

[Iyasu]

tripenfall said:

No, due to backwards compatability the Wii U is the only current gen console where the instruments will cross straight over. New instruments won't be needed for anyone with either GH of RB from the Wii (which is a lot of people). That's going to be the biggest hurdle for people thinking of buying the game on XBone / PS4. That's why this game really should have seen a Wii U release....

Who knows how many of the Wii's Rock Band owners bought a Wii U?
Could be 2 million, could be 2 thousand.

Even if it's the highly unlikely 2 million, it will still cost them more to develop the game for the Wii U than for the x86 consoles Xbox One and PS4.
Also they have to transition from the Wi-Fi Connection to the e-shop. While the process in XBox Live and the PSN are probably the same as last gen, it has changed on Nintendos platforms (how much effort that is I don't know).
I'd guess the benefit of not needing to update the Instruments, as they should already be compatible, doesn't outweigh the risks.