Why don't they wait until fall, and cooler temps across the nation? On July 12 ninety one scooters will head from Bar Harbor, Maine, on a 10-day, 4,500-mile ride to Eureka, California on the ninth Scooter Cannonball

the article on USA Today is very thorough, with interviews, stats, etc. 

To participate costs about 4000, depending on how much a person wants to spend on hotels, food, shipping a scooter to or from either end of the run. 

Plus the cost of repairs, tires, and gas. Things will break, and only some of those might be easily fixed on the roadside. 

I watched a great movie about a 2016 coast to coast scooter ride, Slow Way Home, and it's a hoot https://www.slowridehome.com/

https://www.usatoday.com/in-depth/graphics/2021/07/02/scooter-cannonball-vespa-rally-honda-motorcycle-travel/7507615002/