You act like this is not typical for US stadiums. Sadly it is very normal for US stadiums to not be actually located in the city itself.

AT&T stadium outside of Dallas, which is also hosting, literally does not have any public transit connection to the city. At least they can run the commuter rail to Gillette for the World Cup, and they will also have shuttle buses like they did in 1994. Most tourists will stay in Boston and just go out to the games using the train or buses.

These sort of issues will reflect generally poorly on the state of US public transit in 2026, but acting like it will specifically single out Boston as a “bad city” or whatever is ridiculous. The majority of the US venues are not in urban areas, they are in suburbs outside the stadium. Levi’s stadium is even further from San Francisco than Gillette is from Boston in terms of mileage and is in a different metro area than San Francisco. MetLife is in suburban New Jersey, not NYC.