Didn't a German branch inherit the English monarchy in the late 17th Century? That timing would work out -- people adapting whatever style the monarchs used as the standard.
Elector Georg Ludwig of Hanover became King George I of Great Britain in 1714. This happened because the Act of Settlement 1701 declared Georg Ludwig's mother, Sophia, the heir to the throne (this was done specifically to cut off Jacobite claims), but she died a month before Queen Anne (which was a shame: by all accounts she was brilliant, and she was a patron of the sciences), so the throne went to her son.
I remember when I first started learning German, I thought it was useless. But after getting used to it, when I switched back to English, I was like where are all the nouns? Why is everything lowercase? It's all about what you get used to, I guess.
To maximize information content (entropy), we must try to use all symbols with equal likelihood - which this rule assists, employing capital symbols with closer to equal likelihood than their usual rarity.
Furthermore, said symbols must convey previously unknown information - which this rule does not, as the nouns have the same meaning whether capitalized as not, and the "information" conveyed is redundant.
Human languages aren’t usually concerned with maximal information density though. Multiple layers of redundancy are often present. Features like noun verb agreement, grammatical gender, pleonasms, and even redundant words (last will and testament, vim and vigor etc) are used in various languages despite the redundancy, to increase clarity.
In English, nouns are often spoken with stresses in a sentence, which could make capitalizing them a pronunciation issue, just as other punctuation is (e.g. commas for pauses, question mark for changing intonation). I don't know about German, though.