The views from the back of a motorcycle are much better for seeing the riders up close than any overhead shot. Flying a drone at "rider level" would be just plain dumb. #EasyTargetForCrazyFans.
The helicopter shots are great for seeing the scale of the peloton, the breakaways, finish line sprints and the scenery, but for seeing a rider up close and the pain in their face, or looking back at other riders. Nothing beats the back of a motorcycle.