This test is only for people wishing to drive Black cabs. This test does not exist for drivers other regular taxis in London. Very many taxi companies exist and people are free to drive for those companies.
Uber wants to operate as a black cab without the protections to the fare paying passengers that black cabs offer. For example: all black cabs are wheelchair accessible. Almost no Uber cars are.
I'm not sure how Uber manages to generate so much hype around restrictive business regulation when there's nothing preventing them operating as licensed taxis in London. Nothing, that is, apart from their desire to use untested unregulated uncalibrated software to meter the rides.