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Science. Honestly, that's all the detail I have. The properties of modern rubber don't "leak out" magically after the tire gets hot and cools a couple times, within reason. The rubber you're removing by using the tire is having a much more dramatic effect on the available traction than whether they got up to temp and then came back down.
Have you ever turned your warmers on pre-race, gotten the tires up to temp, and then the skies opened and you had to yank them off to go to rains? I have, and I don't lose sleep over that "heat cycling" causing them to lose grip...and neither should you.