The professional peloton is an incredibly noisy RF environment. Every rider is carrying a two-way radio and a telemetry transponder, every car in the caravan has multiple radio systems, the TV motos are transmitting back to relay trucks with satellite uplinks. Much of a grand tour takes place on mountain roads replete with canyons, cuttings and tunnels.

If you're flying a drone in proximity to the peloton, it's not a question of if you'll lose your control signal link, but how often. I don't know how anyone could operate a drone in that environment with any degree of confidence, even if it's capable of GPS position hold. What happens if you lose your control link just as your battery is running flat? What happens if your chase vehicle gets stuck in traffic and your drone is stuck loitering on the other side of a tunnel? How can a large, heavy drone autonomously find a safe landing place on a mountain stage that's littered with thousands of spectators? A drone big enough to carry the requisite broadcast equipment is undoubtedly heavy enough to kill a bystander.

Broadcasters and race organisers have been using helicopters for decades and know how to manage them safely. Drones simply present too many unknowns. To the best of my knowledge, no helicopter has ever crashed while covering a cycling race. There have been a few incidents where the downdraft from a helicopter caused riders to crash, but none of them were serious.

Semi-pro drones aren't reliable enough. DJI recently shipped batteries for the Matrice and Inspire 2 which failed mid-flight due to a firmware bug. Affected drones fell out of the sky. Most "pro" drones haven't had anywhere near the level of auditing that any commercial helicopter has gone through.