The other thing is that the 'gg' in ggplot2 is the Grammar of Graphics, which describes a high-level grammar for composing visualizations. Having an underlying grammar makes it possible for the syntax to have logical consistency, where once you learn how it works, you can incorporate and generalize simply. (aside, I used to use ggplot2 but I switched to working in python, and I miss ggplot2 so, so much).

The syntax being shown here demonstrates an incremental way of layering on the components of the final visualization, which shows the power of the underlying grammar of graphics.