I would like to know why front drivers side tire tread depth is wore down and not the rest of my tires?
Because your car needs a front end alignment.
Seems like a jump to a diagnosis. The problem could be bad ball joint, control arm bushing (common in Saturns), blown strut or any number of other front end problems including merely a misalignment.
You should have your front end checked.
Thanks I will have it check!