Background: Everybody in London uses Citymapper and nobody uses Google Maps. It is a great app. London Buses are also very good. As has been pointed out, they have GPS sensors. There is also a sophisticated infrastructure behind them, e.g. a control room that tells drivers to turn around and go back mid-rout if the buses are too unevenly distributed. See e.g. the BBC's Route Masters documentary if you can find it: http://www.bbc.co.uk/programmes/b02znsx2
As has also been pointed out here, London Transport does not make a profit (although their public funding is constantly shrinking). So any new entrant has to be more profitable than them with a much smaller market share. Wonder if that is possible if you only differentiate yourself by technology. We'll see.