I think they probably felt that having SteamOS perpetually be the holder for the “most popular” slot in the Linux category is not what the survey is for.
But then, they could have also finally provided a historical chart of OS usage, or a different category for SteamOS altogether.
Could be weirdness, or oversight, or maybe optimistically trying to quietly encourage Linux usage outside of Steam Deck? Who knows.
I think they probably felt that having SteamOS perpetually be the holder for the “most popular” slot in the Linux category is not what the survey is for.
But then, they could have also finally provided a historical chart of OS usage, or a different category for SteamOS altogether.