The point is that it does happen despite planning. It won't happen in the same way in Germany but something else can happen.
The chief architect of the Fukushima plant tried hard to convince his bosses that the wall which protects the plant is not tall enough to protect against rare but possible huge tsunami waves, but hasn't been heard. He turned out to be right.
The plant also had emergency cooling pumps, but the pumps were connected incorrectly. This was unforeseen, I can give you that.
In any case, the Fukushima disaster caused one direct human death, or something like that.
In general, modern nuclear stations are no less reliable than fossil fuel plants, and only freak accidents, like a major earthquake and a tsunami, or personnel knowingly switching off all safety systems (the Chernobyl case) lead to catastrophic failures. This still can and should be improved upon, by using reactors with inherently self-contained designs, lack of high-pressure components within the reactor, etc.
It goes to show that even in developed countries corruption happens and this is a major liability to nuclear plants. If it can happen there it can happen anywhere.
And deaths aren't the only measure of accidents. It also caused major pollution.
I would argue that they were aware and still got hit by the risk. I don’t see “well, that specific failure won’t be what gets us in Germany” as especially compelling.
Given the costs involved however, I find it hard to imagine tepco will make the same mistake again in the next 50 years or so.
(Side note: I am pro-nuclear for baseline load in general. I'm also a realist about how likely problems are to repeat/ryhme.)
They could have protected against this, but siting it near the coast is desirable for cooling purposes too (and has been helpful in some ways for cleanup as they've been able to dispose of waste in the ocean), so there are conflicting concerns here.
Things fail from time to time, if that thing failing is catastrophic, it gets very expensive to ensure 100% reliability.