Had at least 8 sets of Michelins on our tow vehicles and our other vehicles over the years and NONE of them ever had any cracks develop on the sidewalls or the tread areas. One set had a little over 108K on them and still had over 3mm or 1/8" tread left on the most worn area and no cracks but I never run to tires to bald!
Our 1993 2500 truck had 102K on the Michelin tires which replaced the OEM tires when I sold the truck, no cracks! Our 2500HD Diesel CC Long Box 4X4 truck in my signature is on it's second set of Michelins put on 2 years ago and at nearly 200K total on the truck, no cracks! The first set on Michelin 265/75/16 "E" replacement tires on the diesel truck had 97,561 miles on them but were worn to between 4mm and one reading of 3mm and we were going to pull the 5th wheel to Florida as usual so they were replaced, no cracks and I'd even sent several close up pics to a member on this forum of the tires just before replacement which showed they had zero cracks. The OEM Bridgestones on the diesel truck were showing steel belts at less than 40K on them. These 2 pickups were/are only used for heavy loaded RV'ing since they were ordered new.
Neither truck was ever garaged or carport covered either at all and I never have used any "tire shine etc - chemicals" on my tires. Our SUV and the car occupy the garage and a boat is in the 3rd stall. All tires on our vehicles are always kept at max inflation as in like 80 PSI in the "E" tires. Still an excellent ride in the GM trucks at max inflation.
I have no idea what some people do, put on, or whatever to cause their tires to crack. I do know that car washes almost always use tire shine etc sprays products on tires when you get the better higher priced washes as a close friend of ours owned 3 of them and said it's just normal. Most vehicle owners do not even realize this!