When the high-moisture ingredient cooks, it releases steam. This is sometimes unwelcome if you want, e.g., chewy pumpkin cookies, but for foods that already lack a little hydration, it’s a gift.
Article source: https://www.huffingtonpost.co.uk/entry/how-to-make-protein-powder-dessert-moist_uk_6a8d8e74e4b07583705b5785