I don't know if 3 days off is enough to reset things receptor-wise, but the "25 days out of 28" regime was the "old" continuous regime. And yes it was because they thought women should have a bleed every month.
However, there's an interesting angle on this.... coming from Dr Felice Gersh on YouTube if you watch her vids on estrogen dosing.
Essentially: IF you take sufficient estrogen for anti-aging and health benefits, it WILL cause uterine lining build up. It has to, because estrogen is growth proliferative. It's not going to have that effect on one part of your body and not on other parts. So if you want all those optimal health benefits and anti-aging stuff, you need to take decent doses of estrogen and not tiny microdoses which just treat hot flushes and not much else.
AND... if you do take those decent doses, what builds up must come out. As Dr Gersh says.
So it's best to schedule a bleed with a few days off progesterone.
So this whole idea of women being on HRT post-menopausally and on continuous progesterone with zero bleeding, is just not a great idea. Either they are going to be on tiny doses of E to achieve that so the uterine lining is not building up at all, or they are going to have spotting and bleeding randomly problems with many referrals for investigations and hysteroscopies.
Far better to schedule a bleed, know when it's going to happen, and not have unwanted investigations.