[Badger]

You get a couple thousand people out there and there's a lot better chance you're going to find it in the grass or on a sidewalk instead of just one perosn out walking around the city.

Seriously though, it's just an event to get people to donate. It makes as much sense as having a bake sale or silent auction to raise money for AIDS.
It's easier for participants to get donations by having some event that people will sponsor them for. It also a recruiting tool for gathering participants. People are more willing and motivated for something like this as opposed to me saying "Hey, you wanna go ask people for money for AIDS for a while?"