Well, my guess is Romaioi got a really defensible early position and several "stupid" enemies lead by captains (read: The Gauls, Aedui and sometimes Avernii). Placing general to sit down in alpen passage is a nice way to gain good ambush traits, because most Keltoi captains often pass the alps recklessly. On the other hand, Lusotann doesn't have initial enemies, and Kart-Hadast didn't cross anything "choke point" soo often.