The same reason stars or planets don't collide for billions of years. Space is mostly empty and heads-on collisons are rare. So objects usually need to be capt

The same reason stars or planets don't collide for billions of years. Space is mostly empty and heads-on collisons are rare. So objects usually need to be captured into mutual orbit first via 3-body interactions and then slowly move closer to each other via further perturbations or gravitational waves.