A stadium is a service to the public. Stadiums are amenities, and increase happiness among the citizens that enjoy events. Even Sid Meyer’s Civ game has an amenities concept, because they’re really important for cities. If there’s no entertainment options in the city, then all of the talented people leave. That means all of the corporations with great jobs for talented people leave too. With them goes all the money, and you’re left with urban decay and poverty. Yes, transportation is important, but so are amenities.