Perhaps because they thought they were doing a good deed, and had no idea that it would result in a lawsuit. Indeed, as someone else points out, they may have felt the Youngs would be particularly offended by being left out.
It also helps explain why the teens' parents offered to pay her medical bills so quickly, and why the teens sought the advice of an attorney so quickly. It seems reasonable that the neighborhood knew of the Young's tendency to sue. (After all, they had sued their neighbors in the past.)