We all know how the latest treaty worked for the Night elves. The Horde doesn’t keep its promises, the treaty of Azshara was proof of that.
The Horde finds whatever reason it likes to attack, and whenever it wants. It is better the night elves amp up their own defenses than rely on a treaty with a treacherous neighbor. Why would one rely not on their own strength but the restraint of their neighbors?
And let’s not be dramatic about what Ashenvale meant to the orcs. Ashenvale was fuel to the war machine, a spiral of war resources, not food. No orc was starving because they didn’t get Ashenvale’s lumber . There are no farms in Ashenvale either .