Why does the Moon orbit the Earth.

Long/Complicated answer: According to Albert Einstein, The moon orbits the earth because of the differences between the two objects distortion of the space-time continuum. The larger an object is the greater it causes space-time to distort.  So thanks to Einstein’s Equivalence Principle which dictates that it is impossible to tell the difference between a gravitational field and the equivalent uniform acceleration, we can assume that it is not the attractive force of gravity that causes an orbit. It is instead the orbiting object taking the path of least resistance through space-time that causes an orbit.

Short answer: Gravity + Inertia.