There was another similar plant even closer to the epicenter, and it was hit with a (slightly) higher tsunami crest. It survived basically undamaged and even served as shelter for tsunami refugees. Because they had built the tsunami-wall to spec. And didn't partially dismantle it to make access easier like what was done in Fukushima.
Oh, and for example all the German plants would also have survived essentially unscathed had they been placed in the exact same spot, for a bunch of different reasons.
You can't build to withstand humans ignorance. You always can argue to do this or that, but if the responsible managers won't approve it, it's all just theory and good hopes. Even worse if the ignorance grows over time; because the last decades it worked out, surely it will work another decade or two...
That's why things like nuclear are so problematic, because small neglections can explode into cataclysmic events.