(For those who don't know, The Knowledge is a very difficult test that taxi drivers must pass in London to get their license)
I imagine you may have heard about this on the BBC the other day, they did a report on how the government suggested dropping the licensing requirement and the cabbies went, "wait, what? No, that's just trying to help Uber destroy our profession."
I myself had this same question and found that the New York Times offered a not-entirely-satisfactory answer, which is sometimes the best you can get. If anyone can elaborate further, I'd be happy to hear it. The NYT reported here: http://mobile.nytimes.com/2014/11/10/t-magazine/london-taxi-test-knowledge.html
The origins of the Knowledge are unclear — lost in the murk of Victorian municipal history. Some trace the test’s creation to the Great Exhibition of 1851, when London’s Crystal Palace played host to hundreds of thousands of visitors. These tourists, the story goes, inundated the city with complaints about the ineptitude of its cabmen, prompting authorities to institute a more demanding licensing process. The tale may be apocryphal, but it is certain that the Knowledge was in place by 1884: City records for that year contain a reference to 1,931 applicants for the “examination as to the ‘knowledge’ [of]…principal streets and squares and public buildings.”
I'll be saving this thread because I'd be interested if anyone has done scholarship on this subject.