They knew their move was bullshit. They even put a stay on their decision, pending appeal by Trump and following decision by SCOTUS. Trump's team cannot even submit their appeal until 1/4, which is when the ballots go out anyways (state is all mail-in).
They probably put the stay, thinking the headline of thier decision would have wider support, and other dem controlled supreme courts would agree in some way.
The question is since the ballots will have already been sent out, the court might rule the case moot anyways. I hope not, because they would be letting them off their chain for their stupidity. I want the 9-0 explaining how dumb it was, so everyone who came out in support of it is clearly recognizable as a fascist, who supports due process.
edit: btw, here is a piece on this very point. However, many have pointed out this stay in their own decision since the day it came out.