Why are AIs so reluctant to declare war against eachother?

well youve mentioned a couple of things

if you go to the diplomacy screen you can hover over any races youve met to see why a race likes/hates you

if you wait till late game to build up military thats one reason that they will attack you... (this usually works out poorly for them in my games because im spending that time building social manufacturing which swings really effectively to military manufacturing).

difficulty setting may play a role i think at higher levels the ai is more likely to not like you.

there's also a trait that you can choose that will make AI's like or hate you more

 

in my most recent game i was about 200 turns in and only had 1 AI declare war on my and i had no military ships at that time. there was at least one AI war going on with 2 Ai factions both who kept asking me to declare war on the other.

i put 2 pts into the likable trait and built a diplomacy building on each of my planets, then negotiated an open borders treaty with each ai as soon as i met them. 

In my current game with typical large galaxy 8 player (7 random Incredible AI's) Snathi was at war with the Iridium long before the end of the first year.

I know that I play 4x space games quite differently than most and my style is to attack and conquer very early and often. I read a lot of tales of suffering here from players and while a good portion of it is a result of not getting off to a fast start, much of the rest of the suffering is due to not making military ships early enough!

If your military rating is well below a few of the other AI's you may be in for trouble especially at high difficultly levels. If your getting negative diplo modifiers due to being considered weak or worse yet, ripe for conquest, it really is time to get some warships. Ships captured from graveyards can certainly help for a while.

In time I expect the military AI to become a lot better in GC3 and then hopefully we'll see more wars and an even better game. The first step to improve the AI is for it to learn to a drive or two on its ships so they have some decent speed and can actually get to the battle fronts quickly. The next step if for the AI to research Planetary Invasion rather early if it is considering attacking. Then they can really wound or eliminate their targeted victim(s).

Many players wait until they can build nice big ships, but in reality I sometimes find it useful to build Tiny ships early on using my special resources. If the ship gets killed, no big deal as you get the resource back. I don't recall a game where I didn't make quite a few small ships as I lacked the tech to make larger ones until later.

I don't have a problem with the AI attacking me when it thinks I'm unprepared. During my fist games they sometimes surprised me, but now I can usually deal with it quite well.

I don't like the "out of range" wars known from GC II, but mostly because I think it's rather strange - they should IMO make war if they come in striking distance, or are neighboring my sectors, not ages before they can reach me.

But most often these wars against me are the only wars going on for 200-250 turns in my games, with other AIs rarely going to war with eachother in that timeframe. That's what I find too static.

I think the static stuff has more to do with the AI having no idea how to actually finish someone else off. I tried with surrendering on as that seemed to cause empires to shift a bit with random surrendering to other AI but then mid-game when you're strong they all just start surrendering to you so it was too easy to win so I turned that back off.

Way too often the AI all but wipes someone out but doesn't seem to make inroads into their empire. I had one recent game where the AI opponent wiped out the Terrans military, shipyards, everything. Moved one transport in range, then agreed to make peace in diplomacy leaving me to just take the Terrans worlds the next turn (I'd rushed over expecting to split it 50/50 with the AI at best... got it all...).