Why do people think the Earth orbits the Sun?
It's about frames of reference after all. What orbits what depends on your frame of reference.
From The Grand Design by Stephen Hawking and Leonard Mlowdinow:
"Although it is not uncommon for people to say Copernicus proved Ptolemy wrong, that is not true. As in the case of the goldfish, one can use either picture as a model of the universe. The real advantage of the Copernican system is that the mathematics is much simpler in the frame of reference in which the sun is at rest."