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.
Its a lot of work to customise the store for every bit of hardware. The same way that the store suggests pc games if you browse on Mac. Remember, the store Is the same for everyone
I share a first name with a pretty popular fictional character. I tend to enjoy the attention when people don’t believe me or ask if it’s like that one show/book. Fun stuff I gotta say. (thank fuck it’s not a real person that could become racist/transphobic/worse)