I would like to add my theory...
The speedier players who are not too concerned with
keeping a hundred percent solve rate will see a long,
easy-rated puzzle come up and I suspect just pass on it.
Hence some of the easiest ones to solve are also the longest
time wise due to the increase in keystrokes.
And since you only get a max of about hundred and some points
they really arent going to move you up point-wise either.
Hope that helped explain it.
Courage is the art of being the only one who knows you're scared to death.