"To minimise civilian casualties," said Luna. "We can at least give her credit there for not wanting civilians to get stuck in the middle of this, which is precisely why she's not pressing her attack, even if it costs her own forces more. Frankly she seems capable of doing the extra work herself." Luna shrugged at Celestia, "Of course the other theory is that she's preserving both our ponies and infrastructure to use for her own ends later."