And what are the odds in Vegas? How is the opinion of a bunch of gamblers on polymarket relevant?

People are maximally incentivized to be right because of the monetary risk and reward.

A 94% odds indicates an extremely high likelihood that something is going to happen. It's relevant because it's a different, additional perspective than whatever a news article says.

It's a 2500℅ ROI if it's not struck down, so I would encourage you to bet if you think the outcome will be no.

Presumably the justices (or their clerks) have told their friends how they're going to rule, and their friends have told their friends, and that's made the market. Or that's supposed to be the value prop of Polymarket.

There's precedent. Roberts was so angry that someone leaked the Dobbs decision that he spearheaded the investigation that found that nobody would admit to leaking and there's nothing they can do.

Because Polymarket is full of corrupt folks with insider information. Trump Jr. Is a senior advisor to Polymarket. Iran admitted they would observe Polymarket bets during the height of the war to see when they were next likely to get bombed.