My comment said, show me that the Google deal with Reddit is exclusive.

You haven't done that.

And there's no reason to think it would be, because of antitrust. The DOJ doesn't have to act "immediately", the point is that obvious antitrust violations come with fines that make it unprofitable to attempt in the first place. And this would be black-and-white obvious antitrust violation, given Google's monopoly status in search. This isn't a gray area where it might be worth it for Google to roll the dice.