I am ( and I think most ) are replacing tires due to age rather than being worn down. I have not rotated any of my tires and the last time I replaced all 4 with brand new ones I think the tread was probably at 60%. they just got old and two showed real bad signs of dry rot due to sun and moisture.
2015 Palomino Puma Unleashed 351-THSS 37' Toyhauler
2013 F-250 Lariat CCSB FX4 Kodiak Brown Metallic w/18k Superglide hitch and Air Lift rear air ride
"Just put that hammer down and give it hell" -Jerry Reed