I've always wondered this... Maybe it's because PS wants us to roleplay instead of mining (which would be a terrible way of promoting RP). But then how the heck do we get any tria? The only way to efficiently produce money is to mine.
Or maybe it's because no one on the dev team has ever mined before, and they don't realize that most of the people who mine aren't necessarily that intelligent. That kind of labor usually goes to the lower classes, meaning they should not have much education or have a high... mental... whatever it's called... that stat... Yeah. All the smart people are into the whole economic/political thing, or off protecting the state, while all of the mindless, unintelligent lackies are off smashing rocks.