That's the tiny-dataset-fallacy people constantly fall for in the gaming community.
You only think so because right now, no manufacturer puts motion controls front and center with their system. It's the same as the illogical claim that "mobile games killed dedicated handhelds", when we only had two systems (3DS and PS Vita) to back up that argument. So, now the Switch is successful... I guess that didn't happen after all?
And the same goes for the motion control claim: Right now motion controls aren't front and center in most games even though there is a steady stream of releases that use them. But it will only take one single game like a hypothetical Switch Sports to prove the claim wrong.
We can't form conclusions based on tiny data sets. But many claims and theories in the gaming community are entirely based on one or two consoles or console generations to extrapolate realities that don't exist: "Nintendo consoles don't sell!" (data set: Gamecube, Wii U...). "Sony consoles always sell best in Europe" (data set: PS1, PS2, PS4... ignoring the PS3, PSP and PS Vita). "Nintendo consoles always sell well in Japan" (data set: DS, 3DS, Switch, etc. ... ignoring GC, N64, 3DS before the price cut).
The Republicans won the 2016 elections. I guess that means the democrats were a fad after all and we won't see them win any elections ever again.