Why do you think Hemingway chose to show readers the old man's introspective internal dialog?

Hemmingway wanted to give the reader a sense of Santiago without the distraction of other characters. It is both telling and poignant when Santiago unburdens himself through internal monologue. It is as if we are witnessing the essence of the man alone on his skiff. He has no pretense and nothing to hide.

"I wish I had the boy," the old man said aloud. "I'm being towed by a fish and I'm the towing bitt. I could make the line fast. But then he could break it. I must hold him all I can and give him line when he must have it...."