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

[S.T.A.G.E.]

Skullwaker said:
But I thought the Wii U was a casual console.

No. The Wii was the console that was used by casuals and non-gamers (for a short period of time)which accounted for the immense size but still warded off key third party. The Wii U is primarily owned by the Nintendo faithful.