I think that using the "toxicity" excuse is only PR bullshit as there can be options to turn off voice chat as seen in similar games.
In my opinion, they don't use voice chat because the Wii U hasn't got the hardware dedicated to that functionality. A bit like PS3 where devs had to use some of their game memory to enable voice chat in some games so it wasn't present in many MP games on PS3 contrary to X360 that had OS dedicated memory to do that.
It reminds me Mario Kart 8 on Wii U too, in the single player mode, that has to use one whole frame time every second to process the AI of the CPU players resulting in a constant micro stutter (because 2 identical consecutive frames) roughly every second.







