The reason why they didn't attack from their current position was because it was impossible to win. There were walls and readied arms at the perimeter of the capital. However, by going up north and attacking from that direction, they would encounter Dubgall's Bridge which directly led to the capital.
The main point of contention was Dugball's Bridge. Once it was crossed, victory would be in their grasp.
That was what the individuals at the war room likely assumed too. Kazi got a good look at the players that were representing each guild. He sincerely doubted any of them knew the intricacies of Irish history. Even if they did, knowing the specifics of this battle was next to impossible. Depending on the level of the study, they might go along with the instated plan simply due to already knowing that the Irish would win.
But it would take just one person from the enemy side to destroy that confidence and history. One person.