It was for privacy reasons, which is why so many houses are also blurred. Once a house is blurred there's no way to unblur it since Google doesn't take new pictures and as far as I know the blur would still stay at that spot.

Look at every country around Germany and you'll see a web of streets covered by Street View. In Germany it's one big blank [0] and what's covered uses decade old pictures taken before Google stopped mapping Germany on Street View.

[0] https://imgur.com/09Glxyo

I saw a Street View car driving around in Berlin very recently, maybe they have started again?

When you look at that map, you'll see the main cities being covered, but only them. Even rural Romania is mostly covered, while Germany is almost as blank as Bosnia.

Berlin at least still doesn't appear to have any significant added coverage over the past decade. Yes, there are pictures uploaded by users. But the Street View picture seem to be old. In Germany looking at taxis is a good way of telling the age of a picture. All the Street View pictures I clicked on have pre-2010 models. I'd thank they would update the touristic areas or city center first but they seem just as old.

I'd imagine that the privacy backlash is the reason they didn't see the benefit of rolling it out more widely. In most other countries with Street View coverage there's plenty of rural areas covered well. In the UK basically everywhere is included.