You have to understand that diplomacy is far more complicated then seeing who your friends and enemies are. There are multiple factors that go into considering a faction's diplomacy e.g. the faction's interests, their trading partners etc.
Real world diplomacy is like this as well. For example, when state sponsored terrorists attacked India in November, 2008 (I think you can guess which state sponsored this terrorist attack, but I won't name it), India did not go to war with that state due to a multiple number of factors e.g. that state was and still is allied with China (very powerful), U.S. didn't want two nuclear powers going to war with each other and neither did the Indians, India and China are huge trading partners, as is the U.S. and China etc.
Therefore diplomacy is not as simple as faction A is allied with faction B and C who are at war with each other.
One Disco example would be the Zoners. IMO as a former Zoner, the only reason they can remain neutral with the majority of factions is due to their economic influence in regions such as the omicrons which are somewhat resource rich. Zoners are allied to the GMG, who absolutely hate the Corsairs and Outcasts. By your logic Rodnas, the Zoners should go to war with the Corsairs and Outcasts due to their alliance with the GMG, but that is not the case especially because a lot of Corsairs are living in Gran Canaria and because it goes against Zoner ideology to not be neutral.
EDIT: So basically you have to take into account other factors when considering diplomacy.