> many people travel to cities where sports matches, concerts, and other events (e.g., conventions, auto shows, etc.) are held in the stadiums. This also affects other businesses in the city that benefit from the spending done by those that travel into the cities.

So what if City X gets some revenue from away-team fans when the City X Team has a home game? That only evens out with the revenue lost when the local fans go spend their money elsewhere on away games.