Why does the distance between the earth and the sun vary?

The earth is in orbit about the Sun, and the distance varies according to the season of the year. One must also factor in the axial tilt, which explains why seasons are inverted, say, in Australia and parts of South America. if the Earth was straight up and down on its axis- as is often portrayed with globes, this would not occur. The Earth to Sun distance varies between 92 and 93 Million miles.