What would sanitiser fail to do that detergent and warm water would do in cleaning glasses frame that isn't 'visibly soiled'?
The earsocks on Oakley brand sunglasses are made of a proprietary hydrophilic rubber called Unobtanium 1.  From what I can find, Unobtanium is likely a styrene copolymer 2, possibly a formulation called Kraton G 3.  Polystyrene is insoluble in water, but soluble in ethanol and 2-propanol (isopropanol) 4, which are the most common alcohols used in sanitizers.
So, as suggested by @Cell, soapy water is likely recommended by the manufacturer because it is unlikely to damage the glasses, whereas alcohol-based cleaners may degrade the soft rubber components.


https://www.oakleyforum.com/threads/how-to-restore-old-unobtainium-that-has-gone-sticky.10821/
https://www.oakleyforum.com/threads/rubbers.21973/page-2
https://kraton.com/products/KRATON_G.php
https://www.bangslabs.com/common-solvents-and-non-solvents-polystyrene