Having been an organizer at the Summer Olympics and Paralympics, I understand what it feels like to have the whole world focused on the city I have lived in all my life. It makes a person feel really proud. It's kind of like having a big party and inviting the whole world. A good mascot adds to the energy and enthusiasm for the Games, especially among volunteers and organizers. A bad mascot detracts from this energy and enthusiasm.
The cost of having a bad mascot is high. From a licensing and merchandising perspective, people will purchase items with a good mascot on it, but will be far less likely to purchase items with a bad mascot on it. Basically, an Olympic/Paralympic organizing committee can't afford to have a bad mascot, but still they keep coming.
Petra-Mascot of the 1992 Barcelona Paralympics
The first Olympic mascot was introduced at the 1968 Winter Olympics held in Grenoble, France. The best mascots seem to be animals, with a touch of cool-ness about them. The worst mascots tend to be--well, I'm not sure what they are. Some would argue that they aren't bad mascots, they're just mascots targeting little children with the hope that someday they will want to be involved. I should think that a role-model athlete would have a much greater influence over a child's desire to be involved than a mascot, especially if there isn't a noun that describes what the mascot actually is!