We'd love to, but AI doesn't just grow on trees.
And if you think it's too easy, play with Low Resources and Morale Unsteady.
Yes, it can be done.
Of course, I'm open to other ideas as to how we can encourage combat. Though maybe this belongs in another discussion. Personally, I think there are too many high yield mines. The story suggests that most mines on New Terra are the in-game equivalents of one bars and two bars with the three bars in very dangerous areas.
Edit: However, about the spread speed, please remember that if the Blight was any slower or faster it would inexplicably stop moving. So there are technical reasons behind the slow spread speed. Though I honestly agree with you. There should be less ore, more evacuations, and you should be forced to evacuate more frequently. Problem is, that would take a very large map.