It's (unsurprisingly) Apple and Google duking it out and cutting exclusive deals with TV manufacturers. Then the manufacturers say in their ads that they support casting from your phone, but don't specify which phone.
Then there's Google putting out Pixel phones without the hardware that allows you to plug you USB3 into HDMI, so Chromecast is your only option.
Then there's Google putting out Pixel phones without the hardware that allows you to plug you USB3 into HDMI, so Chromecast is your only option.