Why does Coraline go through the door in the drawing room?

Coraline is initially motivated by boredom and curiosity. Her mother is the first to open the locked door, behind which they find a brick wall.
One day, Coraline is home alone and left to her own devices. When she unlocks the door, there is a hallway, and after following it, she finds an alternate universe consisting of a nearly duplicate apartment where her “other” parents speak to her. After she returns home, the brick wall reappears.
In the days that follow, she is alarmed when her real parents fail to return to their real apartment and she finds the “Help us” message on the mirror. Coraline must return to the other apartment to try to rescue her parents and avoid being trapped there herself.