Let me answer as a German with an analogy.
You can compare the German speed limit to weapon ownership in US. Any party suggesting introduction of a general speed limit would conduct political suicide and face serious debates with the automobile lobby and voters (most workplaces here come from this branch). Most rational arguments points towards a speed limit (less traffic jam/noise, environmental pollution...), but similar to US weapon industry, there are to many automobile fanatics in all political parties (either green, liberal, democrats, conservative). You can only lose voters with this topic.
The historical circumstances are simply that a lot of automobile inventions were made in Germany, the car is a status symbol for many here.
These articles sheds some light on the special situation in Germany:
When the introduction of a national speed limit for Germany's
Autobahns (motorways and highways) was discussed in the 1980s,
automobile associations of all kinds demanded the "Freedom of the
roads for free citizens" – with at least some success back then. And
even today, Germany still does not have a general speed limit.
Although a maximum speed of 130 km/h is recommended, where no road
sign expressly indicates this speed limit, drivers can decide for
themselves how fast they would like to travel. If you should pick up a
few angry comments about "Points in Flensburg" during a conversation,
you can be sure that those involved are talking about the
Kraftfahrt-Bundesamt (Federal Motor Transport Authority). Some 7.1
million car drivers are currently listed there. All of them ignored
the signs and were caught driving too fast. The quicker they were
travelling, the higher the fine and the number of points they
collected. Travelling in your own car
Germany is seen as a country of car enthusiasts. No wonder then that
this is where the first motor vehicle was invented. Today, the
automotive industry is one of the country's largest employers. There
is practically no other item that Germans would spend as much money on
as a car. For students, having their own car is generally a luxury.
The prices for petrol and diesel are higher than in other European
countries and the required third-party insurance
(Haftpflichtversicherung) also costs a lot of money. And still, many
afford themselves the luxury of a car of their own.
The German "Economic Miracle" of the Fifties and Sixties were boom
times for the car and road building industry. It was not until the
world oil crisis of the early Seventies that the country's politicians
were forced to contemplate the idea of speed restrictions on
Autobhans. The then West German government reacted by imposing a ban
on Sunday driving and introducing a 100kph speed limit for the
duration of the crisis.
During the 111 days that the speed limit was in force, Germany's
equivalent of Britain's Automobile Association, the 16-million member
ADAC, got wind of government plans to make the restriction
permanent. The immensely powerful organisation responded by promoting
a slogan which has now become part of everyday German vocabulary:
"Freie Fahrt Für Frei Bürger", which translates prosaically into
(Limit) Free Driving for Free Citizens.
The massive public opposition to Autobahn speed limits that ensued
had, until yesterday, stopped the idea from ever being taken up again
by either of Germany's two main parties. Safety has hardly been an
issue either, in fact the government has mounted campaigns stressing
how statistically safe the Autobahn is in comparison to two-lane
The German car lobby, headed by the influential giants, Mercedes,
Volkswagen, Porsche and BMW, has for decades persuaded the political
establishment to reject the idea of blanket motorway speed limits.
To ensure the co-operation of the main parties, Daimler, BMW and Porsche donated a total of 2m (£1.4m) to them in the run up to
Germany's 2005 general election.