Because there is more chaos in organizing an alliance without having an alliance system, because by not having the system it will leave the system to be based more on player diplomacy, and open to betrayal and backstabbing, self interest, and changing sides all the stuff that makes things much more interesting.
Hyboria was not built on long standing large alliances of peaceful countries banding together etc, it was built on the self serving desires of survival and success for you and your people alone. Hence why so many mercenary's are so widely common and utilized in the books.
Because if we wanted people to be divided into two or three sides we would have designed PvP to be around teams or factions rather than free for all.
Because if you choose to be a part of a large alliance you now need to coordinate to make sure you don't friendly fire your own side as not everyone will fit in the same group/raid
Just to clarify here, any secondary or alt characters can still have a prestige class and get the benefits that the class provides to you personally, but your guild will only benefit from the one Prestige class per account to prevent people stocking up mule characters just to get extra bonuses.
So, for example (and this is purely an example, not an actual figure ) if being a Master provided your guild with a % bonus to their resource gathering you wouldnt be able to create x number of alts on the same account to add x% bonus to your guild. I dont believe though that there will be anything stopping any alternate characters having a prestige class.
Forums, 31st March 2006 (Silirrion)
The game will feature clans / guilds and other social elements. The players can build houses, guild halls, PvP buildings. I am not sure exactly what type of buildings the players can construct, structures to raise or plants to sow making it into the final title. Rest assured though, the players can define their own world in a very detailed and personal way in Conan.”
PC.Gamezone, 22nd September 2005 (Gaute Godager)
On a normal server I do not see it being possible for a guild to control a server as they have been able to in some games. On a PvP server the potential for control is greater depending on the implementation.
Forums, 21st September 2005 (Athelan)
To address the question of tabards and whatnot, I believe that we are considering allowing one's guild coat of arms to be placed on various parts of the player's equipment--as well as battle standards--to help emphasize guild identity. I couldn't say exactly where on the priority list this feature would fall, but it's something I would like to see make the final cut.
Forums, 12th August 2005 (Jayde)