Anyways, my fortress is currently at 54 dwarves , and i set all the progress triggers to 1, meaning that sieges can come as soon as i hit 20 pop. Second year, no sieges yet.
Interestingly enough, theres also a necromancer tower nearby. No sieges from him yet, either.
I would expect they will eventually come. I will report my findings here. As i've said, my world consists of one large goblin civ, a bunch of ruins, a necromancer tower, and my fortress. So goblins should theoretically come very soon, because there is nobody else to attack. I will report my findings here and hopefully we can do some !!science!! on the way armies actually work. When i checked legends viewer, it seems that the goblins had been busy creating new dark pits and reclaiming old lost ones.
Keep in mind that the usual requirement for sieges was 80 population, yet some people claim to get sieges in their first or second year... It's truly weird..
EDIT : Okay, i THINK i figured something out. Basically the reason sieges could be rare is because in order for goblins to siege you they need to get in contact with your fortress first. Usually goblins got in touch with your fortress by sending snatchers and ambushes first. Those are gone, so it possible has something to do is that the goblins don't know about your fortress until something happens. I have no idea how or what or anything more but this could be the reason. More !!science!! needs to be done.