The organizers always make this claim. Because I live in this neighborhood, I can attest that it is not accurate. Year after year, there has been trash in the park and surrounding areas. I've attended the event many times and have noticed inadequate handling of the enormous amount of garbage it generates. Receptacles are often overflowing during the event, and it is never "100% clean" afterwards. Period. In fact, I quit going because it sort of kills my buzz to look at trash all over the park and my neighborhood. 

I think the city has been very lenient in the past. A three-year ban will hopefully give the organizers some time to get their act together.