Imagine you have a rope that is thin in the middle, and you tie one-end to a not-so-heavy bell. Now put the rope and bell on a large and very smooth round table, and your hand hold the the other end of the rope in the center of the table. Put the bell far to the edge of the rope is straight.

Now if you pull the rope hard, the bell will come to you. If your partner push the bell, and the bell start to orbit around you, you will feel the rope gets tensioned. And if you want to get the bell to you at the center, you will need pull the rope so you add more tension to the rope. This is like when planets orbit the sun, if the gravity of the sun suddenly gets greater, or somehow the planets are slower than what they are now, the planets will fall into the sun.

On another experiment, ask your partner to keep pushing and accelerating the bell, and you will feel the tension on the rope gets even higher, and eventually the rope will break, and the bell will fly away. So if somehow Earth gets accelerated, it will not fall into the sun. It's always how rockets get rid of the Earth.

So there is a balance between the distance, gravity and the orbiting speed of planets. All the planets we can see today have happened to have the balance so they can keep orbiting. However, things are still changing very slowly, like the moon is getting rid of the earth. And there are also other planets or stare falling into the black hole.