I have a theory about that. I don't think it's due to stretch, but rather, side-plate-gap, i.e., the gap between the outer and inner side plates on the links. More gap means less lateral stiffness of the chain. Once or twice in the life of a chain, I pull the chain off, clean well, and then, adjust the side plate gap with a chain tool. Not so tight the links bind, but eliminating that gap, doing an even job so the amount of pin protuding on each side is the same. Then remount the chain and lube. I don't know if this helps, if it reduces stretch, if it causes any increase in friction when the chainline is off on crossed-gears. I'll have to remember to look at what the gap is from the factory, the next new chain I buy.