1. Because it was not necessary at all.
2. Yeah, that is a bit odd. It made Act 3 a lot easier to do, because the land was a corridor between your country and theirs, so you just push all your units into one territory and go to the next, one at a time. Once I realized that the enemy had basically no land units in the capital at all, I just pushed hard for it. No sweat.
3. Maybe Scarlett just wanted to ride a horse. Or maybe she/the emperor didn't consider appropriating high-tech military stuff for what was basically just a personal mission to be appropriate.
