I think Nintendo used Tegra because it was super cheap. AMD has access to the same ARM cores as everyone else (see Seattle and Sound Waves) but a semi-custom chip would have been more expensive than an overstocked Tegra.

To your point... yeah, Switch was the only 'real' big volume hit for Tegra that I remember (Although I did like my 2012 Nexus 7) with any staying power.

Hell Nvidia was so desperate they did the whole Shield thing...