The dissenting justices say that if there are any remaining issues, like the coffee break question, then the case isn’t moot. Alito’s opinion also references the political brouhaha surrounding this case, explaining:
Five United States Senators, four of whom are members of the bar of this Court, filed a brief insisting that the case be dismissed. If the Court did not do so, they intimated, the public would realize that the Court is “motivated mainly by politics, rather than by adherence to the law,” and the Court would face the possibility of legislative reprisal.
Although he doesn’t say so explicitly, Alito seems to suggest that his colleagues in the majority crumbled under this pressure, writing, “Regrettably, the Court now dismisses the case as moot. If the Court were right on the law, I would of course approve that disposition.”
The “friend of the court” brief Alito refers to did set off a firestorm of controversy, and was dubbed an “enemy of the court” filing by the Wall Street Journal editorial board. In response to this submission, Senate majority leader Mitch McConnell and Republican lawmakers last August sent the Supreme Court a strange letter reassuring the justices that they ought not be intimidated by the rude submissions of Democratic politicians, yet including a similarly menacing message. In the letter, McConnell and his colleagues expressed fear that Americans will be unable to trust the court if the justices don’t go forward and decide the case, despite pressure from Democrats, lest they seem to be responding to politicians’ concerns.