Yeah it’s one line of code to check the user agent but how many lines of code is it to customise each visit to the store front with only content as curated by the device the user is using. Even just user based curation is a lot of work and hard yet they do it because it draws sales. Why the hell would they spend all this work to not show you things. The steamdeck banner is probably considered as part of any promotion internally to the system so not showing it would require filtering every single promotion based on user agent and user logged in.

Trust me. It’s never just “one line of code”