Perhaps you could consider the counter story to your hypothesis.

If virtuallynobody is using the reflective aluminized mylar "space blanket" in clothing, then why is it that the "space blanket" is so heavily promoted as a way of keeping warm by "reflecting body heat back to your body"?

Maybe it is a matter of a little truth blown out of proportion.

It appeals to those who haven't bothered to read very much about the theory of keeping warm ...

I know that the kind of people who sell magnets for healing most of the ailments of the human body also sell "heat reflecting" products to further cure the ailments of the human body.