Adventures was 99% on foot. It's still part of the series. And all the flashy graphics in the world can't cover up a fundamentally flawed concept and bland Zelda-lite gameplay.
You don't seem to understand the difference between a mainline game and a spinoff. Even if SFA was the worst game in the world, it would not have killed Star Fox, because people would have said that it was never a proper Star Fox game to begin with and the quality of the series would be judged on the next mainline entry. Which was the mediocre Assault, followed by the mediocre Command. These are also unsurprisingly the games with the worst sales in the series.
Spin-offs are still part of a series and contribute to its quality. The franchise went from good to crap with Adventures, hence that's the one that killed it. It even introduced the on-foot stuff that dragged down Assault.
And I too hope that Nintendo realise their mistake with Other M; they probably will given its sales, but they might just take those to mean "fans don't want new things" instead of "fans don't want new things that ruin the entire franchise."
I guess Mario & Sonic at the olympics series is killing the Mario franchise then. Worst platform game ever....