If I were to hazard a guess, Valve was apprehensive about releasing the steam machine/frame this year because the high memory prices would mean that they'd have to price the steam machine/frame pretty high as well. However, once they saw how the steam deck was selling like hot cakes even after a $300 bump, they're deciding to go for it anyway.
I guess is was partially the high prices but also their unpredictability.
Having to increase an already high price would not be great.
That is now somewhat better then half a year ago.
Hard doubt they can stock up so fast considering the bump was recent. They planned release anyway