I think you have an overly optimistic view of sea turbines.

They're more expensive, require more infrastructure (pylons and electricity lines aren't conflict free either) and there are a lot of conflicts around use of seawaters. And for a country like Germany there simply isn't enough space within the north sea and baltic sea for all the wind power we'll need.

(And to be clear: I'm 100% supportive of offshore wind energy, I just think it's entirely unrealistic to assume that could be a replacement for onshore wind. We need both.)

Because "as far as possible" is not enough. Even if you ignore that off shore power is a good bit more expensive to build, there is just not enough room there with current technology. And, by the way, the ocean deserves just as much protection as the mountains. Building offshore wind parks is not exactly good for the local wildlife there either.