Earlier quoted context omitted.
On the contrary, recent experience with Olympics and World Cups alike shows that the stadiums often lie fallow, a complete waste of resources. Promised "transport improvements" are often never built in the first place, or built at a level far below what was promised to local residents. Tourism money fails to recoup what was invested.
Exactly. The World Cup being what it is could be played in a public park, and people would still skip their kid's birth to watch it. And yet FIFA insists on a bunch of expensive stadiums each time.
Probably easier to build new ones than adapt old (cf the demolition and reconstruction of Wembley to fix these and other issues.)