If one cared to look at the sets on epay, one might see that a lot of them are in size sequence.
I suppose they are for the dimwits that cannot be bothered to sort out the different sizes. Perhaps they only expect to use just one leaf at a time?
I expect that interleaving thick with thin was started in days of old when people could add up, use more than one leaf and because the sets could be slimmer, use less resources and were cheaper because of that.