2009 CADILLAC STS Wheels Problems

I PURCHASED A 2009 STS IN AUGUST OF 2014. I AM HAVING A PROBLEM WITH THE WHEEL BEARING HUBS GOING BAD. I HAVE REPLACED BOTH FRONT. THE FRONT LEFT SIDE HAS BEEN CHANGED TWICE IN A 13 MONTH PERIOD. UNFORTUNATELY THE PART ONLY HAS A 1 YEAR WARRANTY. I'VE ALSO HAD THE RIGHT REAR CHANGED IN MAY OF 2015 AND NOW IT'S JUNE 2016 AND HAS GONE BAD. I HAVE NO EXTENDED WARRANTY,I'M JUST CURIOUS WHY THIS PARTICULAR PART WENT BAD IN THE TIME FRAME THAT IT DID? I CALLED THE SALESMAN AT THE DEALER ABOUT THE FIRST INCIDENT TO SEE IF HE COULD DO SOMETHING TO HELP WITH THE REPAIR SINCE IT WAS ABOUT 6 MONTHS AFTER I PURCHASED THE CAR. I ACTUALLY BOUGHT IT AT THOMSON AND MCCONNELL CADILLAC IN CINCINNATI, OHIO, OF COURSE HE TOLD ME THAT HE WISHED THERE WAS SOMETHING HE COULD DO. I WON'T...