|Well, in theory, anyway|
Overselling it? Not really. Beyond the traffic and logistics nightmares that aren't really covered by the influx of clueless in and out tourist dollars, there's the real reason why cities push for these: amazing kickbacks from the construction industry to political elites. There is no other reason for it.
After all, it's not as if every area has enough velocidromes (or whatever they call where they race the bicycles), judo and wrestling arenas, equestrian facilities, and so on, and so on. (Or that there will be any use for these facilities after the circus leaves town, no matter what the paid flacks say.) And if a region does have a space for whatever esoterica you can dream up, it can't possibly be up to Olympic / World standards, right? Of course not. Build something new! It's such a boon for the economy. Assuming you define economy in the local, as in local to the tight net of construction related companies that adore your have to have it now now now deadline charging needs. Pay to play. With someone else paying. (Which would be, well, the local citizens.)
This is where, of course, you might wonder why the media isn't pointing out the cesspool of corruption involved here... until you remember that, um, the media is absolutely in the tank for the event. Live sports draws a number, networks want the events to do well either for their property or for the ability to bid for it later, and if you really believe that the news divisions of media companies are ready to bring the tough reporting for their in-house wings, go check how much scrutiny the Washington Post has given to the dirty, dirty world of online education. (Here, I'll save you the step. Next to none, because they own one of the major players in the space. If you want actual journalism on this, you will, of course, have to find it in jokes; try John Oliver's "Last Week Tonight" on YouTube.)
See, here's the thing. All public expenditures for all stadiums are theft. Period. End of statement. Move along. Nothing more to see here. If building a stadium was really an economic boon to the area, team owners and organizations like the IOC and FIFA would not take a dime of taxpayer money. The owners and orgs know this is a money sinkhole. That's why they don't pay for it. But they are happy to tell you why you should, and so is the media.
One of the small fortunate side effects of the massive corruption of media in my lifetime is that people question things like this now, and there's been a small but growing opposition to new pleasure palaces growing across the country. Boston's taxpayers are said to be up in arms to the point of trying to get out of being considered for the Olympics. Brazil's underclass hated the World Cup, and they'll hate the Olympics very soon as well. (Especially when the cost of running them has been wildly underestimated due to massive venue issues based around pollution levels. But I digress.)
In a better world where temporary construction projects like this would never get green lit, the IOC and FIFA would have to play ball and split their events up, hit the same areas over and over again, and in general, act like responsible human beings, rather than howler monkeys. Like, say, rotating it among half dozen different cities that have resources already in place, and calling it a day.
Instead, it gets bid on by worked governments and the corrupt or naive, and a massive bill is left for local taxpayer.
Just like what happens when a sports league needs a new venue!