If they called Python 3 e.g. Cobra or Boa Constrictor or even Turbo/rapid/mega Python or similar nonsense, nobody would likely complain as it would clearly distinguish itself from existing ecosystem and all the enthusiasts could jump on the wave, boasting how much better it is, that it comes from the original authors of Python and then go through usual Darwinian selection to see if they prevailed. But breaking compatibility in a major way doesn't make a lot of people happy, when the gains are small, as with v3.