Well, as @Rinse & rePeat had posted, Dr. Peat gives some insight to what may be the cause:
I heard him talk about it in an interview. He was mostly referring to women after menopause. He said if you are through menopause, have depeted PUFA's from your body and are eating a low PUFA diet, supplementing progesterone isn't necessary. It makes perfect sense, if you aren't estrogen dominant then you don't have anything to oppose. Keep in mind progesterone can cause gingivitis and is precarious for those with diabetes. So it is a wonderful tool for protective reasons, but it does have downsides.
Apologies if I missed it, but can you point me to the quote or video where Ray says that progesterone can cause gingivitis and is precarious for those with diabetes?