Let's just take a quick look at something like VGChartz, even if the numbers are not exact:
Just Dance 2017 PS3, 120.000 units
Just Dance 2017 PS4, 200.000 units.
Just Dance 2017 360, 260.000 units.
Just Dance 2017 XBO, 280.000 units
Just Dance 2017 Wii U, 410.000 units.
Just Dance 2017 Wii, around 1.000.000 units
It's always the version that sells the most.
It's most probably the cheapest version to make, so each unit will mean more revenue compared to other versions.
It's... absolutely insane, but it's the world we live in.
Wii will get Just Dance until it stops being the best place to sell / so easy to make money with; and well...