Maybe because by the time hands were closed into fists, people had forgotten about the negotiating and gotten down to fighting.
In other words, the "fist" symbol was a reserved word for a very different purpose than counting.
Or possibly more realistically: if the way you communicated numbers didn't rely on position to indicate magnitude, you didn't need zeros as place holders. You could just "sign", 3 * 100 + 5 * 10 (whatever the symbols for those were ). Hell, maybe the symbol for 10 was 1 x "fist" and 100 was "pump your first twice."
In other words, the "fist" symbol was a reserved word for a very different purpose than counting.
Or possibly more realistically: if the way you communicated numbers didn't rely on position to indicate magnitude, you didn't need zeros as place holders. You could just "sign", 3 * 100 + 5 * 10 (whatever the symbols for those were ). Hell, maybe the symbol for 10 was 1 x "fist" and 100 was "pump your first twice."