To me it makes sense, if we look at history, steam Linux marketshare went up with the release of the deck.
But the deck is getting really old hardware wise now and struggles with more modern games. As it result, it wouldn't surprise me if many are using it less and less or completely stopped using it for ages.
Then when you combine the fact the newer steam hardware being delayed and deck 2 not coming until 2028 or maybe even 2029 earliest.
It isn't software alone that pushes adoption. The reason why apple MacBook market share has gotten to where it is today is because they keep consistently iterating on good hardware year after year.
Valve need to update their hardware.