Why did the Greeks have different types of columns?

The different Greek columns reflect the evolution of architectural styles over time.
The earliest Greek order of column, the Doric, evolved from earlier wooden models. That is why it is a simpler and stockier version of the other orders of columns. It usually lacks the decorative functions of a base.
The Ionic order of columns originated in the sixth century BCE. Ionic columns tend to be more slender than the earlier Doric columns. They have added decorative elements, such as a stylized capital. This reflects advances in stone working technology and a changing aesthetic in style. As tastes in art and architecture changed, so too did the columns.
The Corinthian order of columns is the most elaborate and decorative of the three. It employs the most stylization of any Greek column. By comparing these orders, we can see that the Greeks had different types of columns as tastes and styles evolved over time. More stylization was desired in later periods than before, and columns evolved to meet this.