This doesn't surprise me in the least. There are a few of these holidays and, when you live in Germany, you have to plan around them and compensate for them. On Sundays, pretty much all you can do is walk, eat somewhere, and buy gas. But only between ten in the morning and maybe six in the evening. And you definitely do not want to try to mow your lawn or operate any kind of electric or gas lawn trimming implement.
Whoever is booking Rammstein probably knew the date of the concert would cause a fuss; consider this a great way to get free publicity.