In short
The two demon-possessed men lived in the tombs, because they served demons, who love death and misery (Matthew 12:43). Jesus’ presence brings the men out of the tombs, because he commands everyone to leave death behind (Matthew 8:22).
The demon-possessed men lived in tombs because the demons, as servants of the great destroyer Satan, love death (see Matthew 12:43). These tombs were typically either caves or other holes carved out of rocks which were suitable as shelter.1 The demon-possessed men emerge from the tombs that Jesus had just commanded his disciples to leave behind on their journey to life (Matthew 8:22).
28 And when he came to the other side, to the country of the Gadarenes, two demon-possessed men met him, coming out of the tombs, so fierce that no one could pass that way.