It's because it's annoying to press the button every single time we get into the car. That's it. A lot of us prefer to drive with the traction control off. If you've upped the power of your engine you run into traction control quite a bit. It also, possibly, saves brake pads.
@JDG, if you don't have the time/desire to do this I can build them and ship em. I'd just need a parts list. I could probably do 10-20 of them just so I could have my own, lol.