Because people who modify their vehicles aren't:
1) The target audience for Subaru
2) The majority of people who buy a Subaru
You're on an enthusiast board, where it seems like everyone tinkers with the vehicle, but I assure you, there are more stock vehicles than modified.
. . .
Yup . . . I guess I would fall into that category. I mean I did add the JDM armrest extension, but other than that and winter tires/wheels that's been it.
Never felt compelled to make any additional mods since a) the car is fine with the way I drive it and b) I'm too cheap to do mods (well that and I have way too many other hobbies and interests so my options are to stop sledding, ATVing, geocaching, etc. and spend more money on modding the Subaru or keep it stock and keep on sledding, ATVing, geocaching, etc.
Besides . . . I kinda hope that when I do sell the WRX in another seven years or so that having it stock may make it a little more attractive to would-be buyers.