That’s funny, I hadn’t thought of that. It very well might be true that turning pages is easier for people with more moisture in their skin.
For touchscreens dry fingers are also called "zombie finger" [1]. The screen registers the too minute change in electrical field as noise and rejects the touch event. Some sweat (but not too much) on the fingers makes all the difference.
[0] https://image.shutterstock.com/image-photo/sponge-finger-wet...
[1] https://www.consumerreports.org/cro/news/2015/06/zombie-fing...
Turning the page is the main thing I do on an ebook, having a button on the side is so much more convenient than touching the screen, I don't obscure what I'm looking at, and I don't smudge the screen.