"A" frame sag, think about it, the higher percent of weight rides on the Drivers side. You have steering box, pump if power, brake booster and master cylinder, alternator, battery, and 200# + driver 100% of the time i'd guess about 300 lbs. only extra's on the passenger side is your spare tire and jack. Makes sense that over time that spring will wear out before the other. Looks like they wanted some tire clearance and while they were at it they raised the difference in the drivers side rather just getting a fresh set of springs.