The current iteration of SteamOS (the one shipped on Steam Deck) is Arch based. So a lot of non-linux users got exposed to it as their first linux distro. Especially with all the emulation guides and other random guides for doing "advanced" stuff to your Steam Deck by dropping in the Arch-ish desktop.

Also anyone who wants to try "Gaming on Linux" needs bleeding edge kernel which is Arch's default setup compared to other distros.