Dane cast 220,000 votes in the gubernatorial election and have already cast 170,000 today. That’s a lot of turnout compared to any other county. Milwaukee cast 340,000 in that election and less than 200k today with less precincts left than Dane.
It's easier to cheat in a single county than in several counties. Plus, you only need to buy off one judge or a handful of county officials. :)
Keep the fraud concentrated, I always say.