We play predefined scripted missions. Those missions therefore are adjusted to a - more or less - specific number of players. For instance: A mechanized mission with aerial reinserts, needs at least a vehicle crew, a pilot and a infantry group. Otherwise the mission can't be played as intended and we go for an other mission or replay.
Those big groups often play missions made on the go with zeus. This means one player is not participating activly but only putting down units, equipment, targets and stuff for the players. Since we are a relativly small group, we dont have such a luxury and it seems fairer to play with a predefined mission, because zeusing often leads to unfair situations and pvp incidents. Zeus is here only used in support for specific needs and not to create a entire mission.
If we want to get rid of LOAs, therefore a rough idea about player number on said event, we also must consider switching to zeus. Without any knowledge of the player number, we cant offer predefined missions with a lot of details, effects and 'love'. Which means one guy is busy an entire evening putting down stuff in hurry, while not beeing able to play. Also zeus has its limitation. You can do certain stuff, but you will never be able to get as much love into details. Even causing a lot of discussion afterwards since someone caused every issue and unfair situation, the mission has.
This is in my oppinion the reason, why LOAs are essential. Besides, we got the reservist system for those unwilling to leave LOAs.