First off, Durant is donating through a foundation, not out of pocket. Second, Kemp is not obligated to donate, and you don't know if this is a publicity stunt aimed at having other ballplayers mimic his actions. Dude's known in the community for his big heart and charitable actions, so he may be (and is probably doing) much more to help the community.
Behavior like this is what kills the good in people, but you're entitled to your opinion.