The Great Gatsby by F. Scott Fitzgerald.

This sentence there is not a comma behind 'and':

"Handsome to look at and a perfect gentleman."

This sentence there is a comma behind 'and':

"Miss Baker's a great sportswoman, you know, and she'd never do anything that wasn't all right."

The author has open hands to write a comma where he wants. The role of the comma is not only to divide clauses in a sentence but wider. If we look at a sentence as music, emotion, and imagination, then we can understand why an author manages a comma like it. The book is a river basin. The sentences are the main river and a lot of tributaries, waterfalls, ponds. Sometimes we hug and sometimes words flow smoothly.

How would you explain to me FSF's style of writing comma on the example of the two sentences above?

From "The Great Gatsby" by F. Scott Fitzgerald.

This sentence there is not a comma behind 'and':

Handsome to look at and a perfect gentleman.

This sentence there is a comma behind 'and':

Miss Baker's a great sportswoman, you know, and she'd never do anything that wasn't all right.

The author has open hands to write a comma where he wants. The role of the comma is not only to divide clauses in a sentence but wider. If we look at a sentence as music, emotion, and imagination, then we can understand why an author manages a comma like it. The book is a river basin. The sentences are the main river and a lot of tributaries, waterfalls, ponds. Sometimes we hug and sometimes words flow smoothly.

How would you explain to me FSF's style of writing comma on the example of the two sentences above?