You do see it sometimes. In many cases its usefulness is reduced by things like terrain, the presence of enemy forces nearby, fortifications, and the RL realities of player response times and activity. If you could count on 100% reaction and movement, then maybe it would work. But units cost money, and you don't want to lose them. 50 good infantry could run you 300 or more gold. Plus banners, siege engines, carts, etc. Units are expensive. Losing a 350+ gold unit to do some small amount of regional damage is just bad economics.
I think that this is actually a very important point.
Dealing economic damage to an enemy should, I feel, be more powerful and cost-effective than it generally is today. For one thing, if a realm is no longer able to effectively refit its army (even though it has not yet lost many regions to TOs), it should be a much stronger incentive to agree to peace.
I've got some ideas for this, but I think that this is probably not the right time and place to discuss them. I'll flesh them out a bit more, and bring them to a separate thread in a while.
