It's because there's effectively a class-action suit going on right now, but because the user agreement says you have to use arbitration, there were tens of thousands of people who are like "sure let's go to arbitration". Valve is losing tons of money having to fight all the suits.
https://www.classaction.org/steam-antitrust-refund-2023
Note: I am one of the people involved in this suit.
Voting for a minor party in terms of the effect on the outcome is approximately equivalent to not voting.