Why did the movie maker choose to make Robert Redfords.......

Why did the movie maker choose to make Robert Redfords character hardly ever say a word at all, to almost never amplify any of his thoughts?. I think one good thing that makes a good movie is when the character can bring you into their world and their mind and way of thinking. This is hard to do when the main character hardly utters a word.

Just because you are in your own private solitary company, doesnt mean its unplausible to make the character talk. I mean yeah....Cast Away with Tom Hanks in would of been so much better if they never made him say anything when he was stranded on that island alone. If they didnt make him do things like run around shouting in joy after he figured out how to create fire the old primitive way.

I aslo wasnt sure about the ending aswell. (spolier below)

When he is sinking to the bottom of the sea because he is obviously too starved and weak to stay afloat, how was he able to hold his breath for that long and still be alive?. When he see's the rescue boat above the surface, he magicly gains a second wind and swims to the top . Wouldent it of been smarter for him to balance that plastic container with flames on top of the water but make sure it didnt float away, than to put it inside his dingy and risk it destroying it?