"They don't have the time or skills" is ridiculous, how comes your fortress gets all the skills, all production and all that while having tons of idlers and high quality stuff after a few years but everyone else is seemingly unable to produce a single good quality roast or any excellent/masterwork item at all. What is wrong with them? There is no infinite desire for beds, crafts, fuel, metal items etc. with no wear + stagnant world population for centuries there would be exactly no demand and stockpiles of good quality items everywhere - the same as it happens in your fortress once you equipped your dwarves, and made all the furniture you need and stay at the population cap for a while. If you add a bit of wear demand will be still very limited (you wouldn't need a large forest to make a few new beds per year).
That's how it is now, not how it will always be.
If there were a somewhat realistic economy goblins would stop raiding/sieges because they can't sustain the continuous losses. I.e. fantasy == no realistic economy.
By that logic, no one would play the lottery. After all, there's only a low chance of getting ANYTHING, and only an absurdly low chance of getting a big prize. Yet we do. Once goblins actually raid settlements they destroy, it'll make sense,
Alternatively, dwarves and goblins hate each other. That's plenty of reason for war.