Kids. I think the answer is kids. Those other major sporting events are mostly adults. Disney, in comparison, has a much larger portion of kids who visit. Even though the race may be adults, people come with their family’s and the parks will be packed with kids. Kids that largely aren’t eligible to get vaccinated. While transmission is much lower in children, it does exist. As does the Misc-C complication. As the spread in adults slows down with vaccinations rates, and the next phase focuses on children, so to will the news media. I think for all those reasons, Disney is going to be extra careful about any potential “outbreak” headlines as well as any perceived failings on safety measures.
While I follow your reasoning, this is Disney. It's packed with kids every day. You really think that the kids that will come woith their families for the race weekend causes a greater amount of concern than the kids that will come any other day? For Christmas? For the Halloween party stuff? That doesn't add up to me.