Always porting not-yet-upstreamed patches to new release kernels is additional work to the upstreaming work towards the latest development tree. The Valve engineers interviewed around the very first Steam Deck announcement said their goal with moving from Debian to Arch was to minimize the patchset maintenance burden. Their approach surely has that goal in mind. There are only two variants of Steam Deck with minor differences between them. If backporting patches from newer kernels is less work than forward porting their patches, they just stay with that version for a while. Updates to drivers for hardware they don’t use and filesystems they don’t use aren’t relevant to them anyway.
Always porting not-yet-upstreamed patches to new release kernels is additional work to the upstreaming work towards the latest development tree. The Valve engineers interviewed around the very first Steam Deck announcement said their goal with moving from Debian to Arch was to minimize the patchset maintenance burden. Their approach surely has that goal in mind. There are only two variants of Steam Deck with minor differences between them. If backporting patches from newer kernels is less work than forward porting their patches, they just stay with that version for a while. Updates to drivers for hardware they don’t use and filesystems they don’t use aren’t relevant to them anyway.