Hmm, I replied yesterday but apparently mods never approved it.

The stages usually run in pretty remote areas, so mobile connections simply don't work well enough (yet). Especially as they get blocked by the fans if they work. I think some privateer tried that in Monte 2-3 years ago, but most of the time it didn't work.

For broadcasting normally you would need a helicopter above every car you want to broadcast, a plane above everything and a satellite connection. So that would be even more expensive than a normal live stage with 1 or 2 helicopters.