The t-shirt that they give only to people who finish is a big reason that so many people take up the challenging race.
This paraphrase presents the same information as in the sentence, but since it should be a bit more of a summary, it takes out the specific detail of how many people actually run the race, which can just be paraphrased into 'so many'.
The kite belongs to the girl.
The job that belongs to mom.
The dish that belongs to the cat.
Emotional appeal, as this will trigger emotions and potentially persuade the viewer in the end.