they will never cancel it on the wii if you look at the statistics it and the xbox 360 has sold more starter packs on thoes two systems than any other one besides the ps4 xbox1 and the wiiu are garbage
The Wii has been outdated since it came out, and whilst it had the motion control appeal back in 2007, that phase has passed. Publishers only published for the Wii because it was the top selling system, but now Wii owners are finding themselves with low quality ports of games designed for the PS3 and 360. Swap Force was a perfect example of this, and it was kind of a wake up call for a lot of people that they might need to consider upgrading.
Doesn't have to be anything fancy either, you could get an Xbox 360 Arcade (the cheapest model - it was even cheaper than the Wii when it launched) that'll play any version of Skylanders just fine.
And whilst the PS4, XBO and Wii U might be "garbage" in your opinion, they're the newest generation of system and Activision would be foolish to abandon them now. Just because the lowest selling versions of the games were on new systems doesn't mean they shouldn't release them on those systems, it means not as many people own these new systems... Because they're new.