While messaging how much they might make from posting affiliate links would be good for the affiliate, I can see it being sometimes undesired on the dev end. Primarily if they have it set to zero until they get into the black, it might become bad PR if [the info on revenue cuts] is spread around to the general public.
An idea: if in the settings for itch.io cut, there was a sub bar for affiliate cut [not unlike the humble bundle devs, charity etc. sub bars] and if the affiliate bar is non-zero a tick box appears for if you want to display the affiliate revenue to affiliates. That way it's an opt-in process.