To connect with his audience. Personal stories make him seem more relatable.
He tells personal stories as a way to illustrate his points. For example, if he's talking about the importance of family values, he can use his own family experiences to drive the message home. Also, in the political context, it helps him to build a more personal brand, differentiating himself from other politicians. By sharing his own story, he can show where he's coming from and what his core beliefs are based on.