Well, part of why the Wii U is doing badly right now is because they didn't keep enough secrets.
The reveal of Mario Kart 8 and Super Smash Bros 5 caused many people to decide to wait on buying the Wii U.
Think; for example, why would many people get New Super Mario Bros U when you know Super Mario 3D World will come out.
They are very similar but 3DWorld is in 3D while NSMBU was 2D.
Games that seem like Prototype Varients of other upcoming games just are not going to be popular.
Like if Sakurai announced SSB6 for the Wii U before SSB5 comes out, why would anyone get SSB5, they'd wait for the most likely to be superior SSB6.
And do you think Melee would have been so popular if another Smash Bros game for the Gamecube to come out in 2004 was announced before the release of Melee?
I think most definently not.
If people knew about Mario Party 2 before Mario Party 1 was released, then they would all just hold out since Mario Party 2 was both vastly superior, very similar, and only a year out.