The only reason I can think of, is that the " paper+pencil+sealed cardboard box" solution isn't good at giving lucrative contracts to buddies of election offici

The only reason I can think of, is that the " paper+pencil+sealed cardboard box" solution isn't good at giving lucrative contracts to buddies of election officials. The "speed of counting" argument does not hold : in Canada we get the final results of elections just a few hours after the closing of the vote. Tallying is all manual, and the counting of each box is done under the supervision of members of antagonistic parties.