Interesting point. I’m old enough to remember when people only shampooed like once a week. It might have been the introduction of Herbal Essence that ushered in the idea of frequent use. Heck, anyone remember 5-Day Deodorant Pads? Wipe your pits on Monday and your good to go for the whole week.
Some scientific type pinpointed the bacteria that produces body odor. Then he developed a wipe that knocked them right out. He went, undoubtedly in Birkenstocks, for several years without bathing or smelling bad.
From what I read elsewhere, though, eradicating underarm bacteria isn’t the end of the story. Bacteria from other parts of the body will eventually take over the vacated real estate and you don’t want that.