If there had been more stages, we still might not have got much more stage kilometres as more stages could have been cancelled. If the stages would have been splitted into halves maybe neither half could have been run.

Having 3 stages a day means obviously a bit less to follow, but for tv (if someone outside France bothered to show it) it's better as they don't take quite as much time. Also, variety is nice, so I think it's good to have an event with only long stages.