They have different objectives honestly. Miracast was supposed to stream frames exclusively. Chromecast hands datastreams to the target device who then has to do the heavy lifting, sometimes even fetching the source itself. Entirely different use cases and tech stacks. I would like to show my PC screen on the living room. I can’t do that without paying either Google or Valve (still Google), despite the fact it is not technically difficult or complex with contemporary technology to stream raw frame buffers to a screen. But that’s patent trolling and monopolies. They will sap all the fun out of tech for those extra pennies.