When to replace tires?

FWIW. I just got my Michelin Energy Saver A/S replaced. Ran them suckers to the wear thread especially after it got a bit squirrelly on Thanksgiving Day in SoCal rain. Only got about 40k or so miles out of the 65k warranty. Couldn’t even attempt to take it in to Costco due to inner tire wear out on all tires. Still wondering how that came about. Not sure if it was due to rotation @ 10k after the Toyota freebies thru 25k or there’s really something wrong with my cars alignment which I find odd. Anyways it’s on some new set of the same Energy Saver A/S. Time to keep and eye on it and hope for the best.