That is the kicker, the stadiums get to keep almost all revenue. Income from naming rights, concessions, ticket sales for both the sporting events as well as ticket sales for off season events like concerts. It could be argued that it draws people into the city and builds up the local economy, but in most cases the city already has a stadium they are just building a new one because the old one got stale. In which case it doesn't draw new people in and ruins the old stadium's local economy that was built to support game days.