Not entirely sure if it is a insurance driven reality but as you know yourself better anyway:
We never had that many cars build in the 30s, 40s and early 50s as in the US (due to the sheer market size, the overall road reality, the market place as such and many very often unfortunate and sad reasons). So there are not that many leftovers available in the first place.
Adding to this, Germans are obsessed with cars, but new ones. So there isn't a real market for vintage car oriented wrecking yards. Hence, old cars were mostly totally disposed of. Owning a vintage car is mostly seen as a quirky and useless hobby (which it actually is :-) conducted by either a. the rich (vintage European cars tend to be expensive; this type of customers would not go to wrecking yards) b. the nerds mostly interested in the US culture for various reasons (that would probably be me; they would not find anything over here anyway due the sheer lack of US cars) c. European nerds (only interested in 60s, 70s European cars) and a few show offs (for whatever reason you have to own a muscle car these days if you want to be perceived as a successful person in the world of marketing over here (or so it feels :-)). In any case it is a small market.
Plus - I guess - wrecking yards are missing the cool factor over here. They are not perceived as male play grounds and adventure havens, but as a location for poor, useless people who can not afford to purchase the stuff somewhere else.
And probably finally - Germany isn't that big and therefore land isn't that cheap. What I mean to say - wrecking yards that I have come across in the US are often hugggeeeeee, spacious, but out in the sticks. This kind of "out in the sticks" we rarely have and if so it is probably still too valuable to be covered purely with "chunk" to be visited by a hand full of people on a daily basis. Probably wouldn't be worth the investment.
That's it . . . :-)