Their advice in the little instruction pamphlets that came with their DEs also recommended waiting about 2 minutes after applying the cream or soap, to let the stuff soak into your beard. I do that, but have increased it to 3. They did indeed know their business. Then.Interesting question, I think it was more of a evolution in shaving. I think barber shops who did straight razor shaves for their customers used hot towel application to clean the face and soften the beard. Then applied the lather and started the task of shaving. I have used the hot towel method but prefer to brush wash my whole face with CeraVe hand bar cleanser for great face feel during the brush massage and post feel.
Gillette pamphlet I read once states to clean face of dirt & facial oils first (defoliate) and then apply lather so that is what I do, Gillette did a lot of good research in the Golden years of shaving to get good results for their products.