Not all the launches will aim to sent people to Mars. Some will just send cargo, and some will send stuff to LEO.

FTA:

  Musk said that the spacecraft is being designed with the plan of flying [..] a total of more than 1,000 flights per year, per vehicle.
  Ultimately, Musk says that he hopes to achieve [...] a goal of hitting 1,000 in total in service over the course of the next decade. 

So that's one million launches. That's corroborated by the goal of 100 megatons of cargo per year (given that each Starship can carry 100 tons to space).