That ruins the whole point of difficulty setting. What's the difference between Easy and Legendary, besides the block count, with this suggestion? There is a reason Legendary is so hard - it's because only the very best are supposed to finish it. If you can't handle it and rage, thats why there are easier difficulties.
With your suggestion there is no punshiment for falling rather than being thrown back a few blocks until last checkpoint. If we add this then everyone would be completing Legendary 24/7.