"Because their goal is here. If we try to meet them elsewhere, they'll split up and prevent us from interfering with awakening the slumbering Heretic God. It will also spread out the damage over a larger area if we do. And like the young miss Mariya said, our goal is to delay, not defeat them. Acting aggressively only gives them an advantage over us acting cautiously. Given the fact that the 5th Campione will be returning as soon as possible, not to mention his spotless record as far as collateral damage goes, if you are taken as the average that is. The rules of this engagement are simple: revive the sealed god or escape before Shirou returns and they win. We remain here to prevent the first and the second condition won't be fulfilled until the first is complete, otherwise Guinevere would never have come in the first place. She would have sent a representative rather than come here herself."
