Here's why:

* Gravity is a fundamental force: It's the force of attraction between any two objects with mass.

* Earth's mass is huge: The Earth has a massive amount of mass, which means it exerts a strong gravitational pull on everything around it, including airplanes.

* Airplanes have mass too: Even though they're flying, airplanes still have a lot of mass.

* Gravity pulls everything down: The Earth's gravity pulls the airplane down towards the ground. The plane only stays aloft because of the lift generated by its wings.

It's important to note: The airplane doesn't "pull" on the ground. Instead, gravity pulls the airplane towards the Earth. The Earth's massive size means it doesn't noticeably move in response.