1. Because I'm too cheap/lazy to go to the store and buy it for $40 ($60 if you include the expansion pack). I'd rather wait a few years and buy it for $5... I almost never buy games new.
2. Because, from what I hear from friends who have played it, it ain't got nothing over Civ 2.
3. Because I already have too many computer game obcessions already.
I'm not married yet, but when I do get married somewhere down the road, I would want to find someway juggle Civ 2, SFCII, ADOM, *AND* my wife without another game getting in the way. (Not tonight, hun... I'm too busy playing Civilization 3!)