If erlang law said 1 channel = 1 traffic unit, and 100 channels = 100 traffic unit, and be very linear, then it would be useless, and this forum wouldn’t even exist :=)
Might be because of small difference in traffic increment causes a large difference in channel increment, as channel increases. Similar to diode characteristic curve. You dont want to write large numbers, so log scale is a good choice. Thats my guess though.