Why doesn't Canon (or Nikon) make their flashes radio-wireless-capable?

I originally thought RadioPopper JrX can support ETTL but I now realize it's manual and that's why it's affordable.


I think I still like RP PX the best. But the requirement of having a master on camera is making the setup not convenient and heavy.


PocketWizard's FlexTT5 seems to have issue on interference.


So everything nails down to the ultimate question:


Why doesn't Canon make their flashes radio-wireless-capable?


I assume Nikon's flashes also need to "see" each other in order to communicate wireless? No?


Please educate me!