Two massive hurdles to doing that live.
1) Reliability, its not good enough to get it right some of the time whilst shooting a video (each shot only being 3 seconds or so and you get unlimited re-takes), you’ve got to film 200 riders down the hill for 3-4minutes each, without hitting a tree or worse the rider, or even being close enough to distract them, and do it on any track.
2) Transmission, getting uncompressed HD video transmitted reliably is tricky (its about 3 Gbs), most commercial drone filming relies on on board recording and the link to the controller is just a preview. It can work (its used a lot now for news and sport) but you have to work within the limitations, mostly that it only works line of sight, you won’t get a good enough signal over long distances through the woods.
Same reason they don’t just stick a helmet can on them all.