They don't.
You've been nicely brainwashed by the media, there's a few very rich people who pay a lower percentage. that is not the norm most people you consider to be rich, are payee just like us and can't not pay less.
And there's plenty of self employed/contractors who pay less tax percentage than payee people as well.
I don't think that's the story the media is reporting. I think the media is more interested in telling me about scroungers on benefits or Romanians with a crime wave.
And I agree, I know a lot of contractors who pay less tax via personal service companies. That is a problem with the tax system too...