Harder puzzles need more calculation and more time.And it's easier for us to do the wrong moves.I suggest harder puzzles should be higher valued,such as if +30 for a puzzle which has normal difficulty,and+40 for a harder one,+50 for and extra harder one,and so on.This would encourage users to challenge harder puzzles,because they can have more scores in reward.I hope that this forum will seen by the chess.com stuffs.