I think they're literally just shoving shit out the door as fast as they can, and their initial production runs were ... kind of done in the middle of rampocalypse/tariff nonsense, round #(i forget).
Because you'd have to be an idiot to not realize the world economy is headed for a Great Depression, therefore they need to make money ASAP on hardware, before people's budgets contract dramatically.
I also think they seem have to have just genuienly underestimated demand.
I don't think we'll be seeing newly made Steam Decks soon, iirc, they retooled the actual Steam Deck facility ... to make the Steam Controllers.
Probably more likely to see the Steam Machine and Frame, and then a Steam Deck 2 at some point in the future, presuming we do not at that point live in the Fallout timeline.