2004 Mazda 6 Premature Tread Wear in each of last four year

Mazda 6 Sport Wagon (2004, V6, A/T, Size of tires is 215 50 17) needed tires four years ago, when my one-way commute to work was 48 miles one way, five days a week. Local national chain tire store has a knockout sale, at that time, on Sigma Regent tires. Four installed. As in the past, and ever since, oil changed every 3,000 - 4,000 miles and tires rotated by same national chain's personnel every other oil change. Sigma Regents came with a 70,000 mile warranty. After 24,000 miles of usage, the treadware on this was 2/32's (or so) and same store, found no signs of any abuse or neglect by the owner (me) since all of the checking and rotating and spin balancing of the tires were always done at that same store. For new Yokohama AS 430 tires with 60,000 warrant were provided just one year or so after Sigma's first put on. The ride, performance, reliatility, handling of hte Sigmas, and of the Yoko's were great. Exposing these tires to Pennsylvania roads and weather. Another 13 months or so passed, and this time the tires treadwear after just 24,900 miiles put on the AS 430 tires had diminshed to the point that my Mazda dealership would not pass the vehicle for State inspection withouth four new tires! Again, local tire store seeing throughout the prior 13 to 14 months that the treadwear was again never going to make the 60,000 mile mark, provided no resistance and awarded what appeared to be a fair 'allowance.' Again four new Yokoahama AS 430's put on with a 'fair' allowance being provided by national tire chain store. And thereafter car quickly passed inspection. Six months later, and now driving about 4,000 miles per month to a different job, same tire store manager agreeing that this set of AS 430's also NOT going to last even three more months! My dealership, my tire store managers (visited THREE stores in same chain) not others can pinpoint cause of premature tread wear in the absence of any other signs of neglect or abuse on any of these tires. Now, with a somewhat fair 'allowance' being provided, I'm being told the newest management team at this national tire chain store that (a) I never should have been put into either the Sigma Regents or the Yoko As 430's and (b) their suggestions are for me to consider the Sumitomo Touring LSV tires or Uniroyal TP Touring (New Tread Pattern) tires. Suggestions? Changing tires every 13th month or so is troubling !